Desmond becomes unstuck in time while traveling to the freighter, and there’s only one person in the world who can anchor him before he is lost forever: Penny.

Written by Carlton Cuse & Damon Lindelof
Directed by Jack Bender

On its way to the freighter, the helicopter is forced to fly straight into a thunderhead, and the strange temporal properties of the island cause Desmond’s consciousness to flash backward in time to his days in military service in 1996, after he broke things off with Penny. But there’s an even bigger problem: Desmond’s memories have reverted to where they were in his past; he remembers nothing about the present. From his perspective, he’s flashing forward to the future, and he has no idea what any of the things going on, on the island or on the freighter, mean. He freaks out, and Sayid is forced to restrain him until they land on the freighter (which is named the Kahana).

At the beach, Jack and Juliet grill Charlotte and Daniel about what’s become of the helicopter, believing the two of them to be holding back crucial information. Daniel finally reveals to Jack and Juliet that their perception of the passage of time on the island is different than the way time passes outside of the island. He suggests that there may not be any problem at all, because the helicopter may not have actually been gone for a full day, even though it seems that way from the island. But he does warn them that if Frank deviated from his flight path of bearing 305, then there may be side effects.

When the helicopter lands on the freighter, it’s greeted without warmth from the crew, most notably from an aggressive, belligerent named Martin Keamy. Desmond continues to freak out over his memory loss, but Keamy and the Kahana crew seem unsurprised by what’s happening to him. They take him down to the ship’s sickbay to see the doctor. There, he meets George Minkowski, the man Jack and Kate first talked to over the satellite radio. He’s strapped down to a gurney, and asks Desmond if “it’s happening to you too.” George goes into a sudden catatonic state, and is unresponsive to Desmond, but then he wakes up and explains he was flashing around through time the same way that Desmond has been. The doctor enters and sedates George, despite George’s desperate protests. The doctor then turns on Desmond and examines him.

Out on the deck, Sayid trades his pistol for Frank’s satellite phone, so he can make a quick call back to the island. Jack answers there, and Sayid explains over speaker phone what’s going on. Daniel asks if Desmond has recently been exposed to high levels of electromagnetism (which of course he has, when he activated the failsafe and destroyed the Swan station). He explains that for reasons he doesn’t understand, some people suffer mental trauma when coming or going from the island.

Desmond returns to his past in the Scottish military, but remembers seeing a photo of Penny in his flash forward, so he goes to a telephone booth and calls her up, hoping she might be able to help him sort out his confusion. But she’s still hurt by the way he ended things with her, and wants nothing to do with him. He suddenly returns to the present on board the freighter, where the ship’s doctor is examining him. Sayid and Frank burst into the room, and give Desmond the satellite phone over the doctor’s protests, saying that Daniel wants to talk to him. The doctor sounds an alarm, so the phone conversation must be brief before they’re interrupted, but Daniel quickly tells Desmond that the next time he flashes back to the past, he needs to go to Oxford University’s Physics department and visit Daniel there, because he worked there in 1996. Daniel digs out a well-worn journal from his belongings, and uses it to give Desmond some important instructions: Desmond is to tell Daniel’s younger self to set his “device” to a very specific setting, and if that doesn’t convince Daniel of what’s happening to Desmond, then Desmond is to mention that he “knows about Eloise.” Keamy and his pal Omar break into the sickbay just then, but they’re too late because Desmond already knows what he must do.

Desmond returns to the past again and follows Daniel’s instructions, visiting Oxford University to meet an eight-years-younger Daniel Faraday. Younger Daniel doesn’t believe him of course, angrily assuming that his colleagues on staff at Oxford — who apparently think of Daniel as a crackpot scientist — are playing a prank on him. But when Desmond recites the information present-day Daniel told him to pass on, Younger Daniel takes him to his laboratory. There, Daniel conducts an elaborate experiment using high concentrations of radiation fired upon a mouse named Eloise, who is placed in a custom-built maze. The idea behind the experiment is to “unstick Eloise in time,” just like Desmond, but Daniel uses the precise numbers given to him by Desmond to make it work. As they watch, Eloise the mouse goes straight through the enormous maze as if she’s done it many times before — but Daniel then reveals that he only finished constructing the maze this morning and hasn’t taught the mouse how to traverse through it yet. He explains that he knows the experiment worked, because Eloise’s consciousness just traveled through time to the future, where she’d already been through the maze, and came back to now with memories of how to do it.

Desmond returns to the future, where Keamy takes the satellite phone out of his hands and forces Frank to leave Desmond and Sayid locked in the infirmary alone with George. Before they go, Sayid requests a meeting with the ship’s captain, and Keamy says he’ll pass along the message. When they’re alone, George pipes up, explaining that he knows who Desmond is, because he monitored repeated incoming calls from Penny that the Kahana crew was instructed to ignore. (These calls culminated with Penny’s conversation with Charlie just before he died in the Looking Glass station.)

In the past again, Younger Daniel notes that whatever effect is causing Desmond to jump back and forth through time is increasing in strength, making it increasingly harder for him to get from one to the other. Desmond notes that Eloise the mouse is dead, and Daniel explains that her brain short-circuited because jumping through time left her mind unable to tell the present from the future. In order to prevent the same thing from happening to himself, and to stop all of this jumping around once and for all, Desmond must find himself an anchor, or what Daniel calls a Constant. A Constant is something familiar that exists in both times, something with deep personal meaning to Desmond, that he cares about profoundly. Desmond knows instantly what his Constant is, the thing he cares about most: Penny. But Daniel cautions him that he’ll have to make contact with her in both time periods for it to work.

Desmond flashes back to the present, where he asks for Sayid’s help in calling Penny. George warns them that someone on board (who we know must be Ben’s mole) sabotaged all of the ship’s equipment used to contact the mainland. George offers to fix it if they can get him to the radio room, and suddenly the three of them notice that the door, which had been locked only a moment ago, was now standing open.

In the past, Desmond visits his nemesis and Penny’s father, Charles Widmore, who is attending a private auction where the only known artifact from the Black Rock, a journal written by the ship’s first mate (see below), is being sold. Widmore wins the auction after a fierce bidding war, and pays a hefty price for it. Desmond asks him for help in reaching Penny, because she’s disconnected the only phone number he has for her. To Desmond’s surprise, Widmore actually gives him Penny’s new address.

In the present, George carefully leads Desmond and Sayid to the radio room, but George goes into another time flash and dies before he can fix the radio. Sayid steps up to rig the radio himself, enabling Desmond to make a single call, but Desmond doesn’t yet know Penny’s phone number.

In 1996, Desmond rushes to the address Widmore gave him, and begs Penny to give him her new phone number. She’s uninterested, but he begs her for the number, promising not to use it for eight years. Penny’s incredulous over his bizarre claim and even stranger behavior, but he appeals to her on an emotional level, pleading with her to believe that the two of them might still have a future together someday. She gives him the number on the agreement that he’ll leave after he gets it, and he begs her that when he calls her in eight years, on December 24th, 2004, to please answer the phone. But she throws him out of the apartment, fed up with his seemingly crazed rantings.

In 2004, Desmond has the phone number and he recites it to Sayid, who punches it into the radio. Desmond’s memory rushes back suddenly when Penny answers and he hears her voice. The two of them can’t believe they’re actually talking to one another after Desmond’s three year marooning on the island, and they engage in a very emotional telephone reunion. Desmond is relieved that she still cares about him, and Penny reveals that she’s been trying to find him for the past three years. She somehow knows about the island, and that he’s been on it. The signal starts to die, and Desmond professes his love for her, and she reciprocates. Just before they lose the call, they pledge to one another to never give up on finding a way back to each other. Sayid apologizes that the power source went dead, but Desmond tells him it was just enough.

On the island, Daniel reviews his journal, which is filled with cryptic equations. But one page in particular catches his eye, a page upon which is written, “If anything goes wrong, Desmond Hume will be my Constant.”

    • The island seems to be surrounded by a strange time/space anomaly that not only shields it from the outside world, but makes traveling to and from it very dangerous.
      Question: Ethan told Juliet that her journey to the island would be intense, and then later he strapped her into a bunk in the submarine, explaining that “the last leg is always a little bumpy.” What is it about the island that makes journeying there so difficult and fraught with danger? [3.16]
    • Nope. Penny’s heart now and forever belongs only to Desmond.
      Question: Did Penny ever get married? [2.24]
    • Penny does know about the island, but how she found out about it and how much she knows is unknown.
      Question: Does Penny know about the island? If so, how? [2.24]
    • The unusual properties of the island cause it to somehow be out of phase with the rest of the world. The helicopter arrived safely on the freighter, but it was a day later than expected.
      Question: The helicopter hasn’t been seen on the island or the freighter for more than a day. What’s happened to Sayid, Desmond, and Frank? [4.04]
    • Though the details still aren’t entirely clear, the freighter knew of Desmond and Penny’s relationship largely because Penny has been sending regular signals for a while now, trying to reach Desmond on the island.
      Question: Why did Naomi have a picture of Desmond if she wasn’t there to rescue him? [4.03]
    • Minkowski had fallen ill from the same time-jumping affliction that threatened Desmond’s life, and was secured in sickbay to protect him and everyone around him.
      Question: Why was Minkowski unable to come to the phone when Miles called? [4.02]

    • How did the journal belonging to the Black Rock’s first mate get to Madagascar after the ship wrecked on the island?
    • Tovard Hanso found the Black Rock journal and kept its contents secret for over a century. Is this journal how Alvar Hanso found out about the existence of the island, and decided to place the Dharma Initiative on it?
    • Why did the Hanso family decide to sell the Black Rock journal in 1996 after years of keeping it a family secret?
    • Why is Charles Widmore so interested in the Black Rock? Does he know about the island? If so, how?
    • Why was the freighter instructed to ignore Penny’s transmissions?
    • How did Penny know about the island, and that Desmond was on it for three years?
    • What’s the meaning of the phrase in Daniel’s journal, referring to Desmond as his Constant should anything go wrong? What did he think might go wrong, and why did he choose Desmond as his Constant?

    It would appear that the prolonged exposure to radiation in his Oxford lab is the culprit behind Daniel’s memory problems. This was implied, though not confirmed.

    The Black Rock set sail from Portsmouth, England on March 22, 1845, on a trading mission to the kingdom of Siam. But she was lost at sea, and instead wound up on the island. Somehow, the personal journal of the ship’s first mate found its way to Madagascar, where it was discovered seven years later by an ancestor of Alvar Hanso — financier to the Dharma Initiative. Until 1996, the contents of the journal had never been revealed to the public or anyone outside of the Hanso family.

    The word momentous barely does justice to the many events that unfolded in “The Constant.” The biggest of course is Desmond’s emotional conversation with Penny by telephone, but this ep also marks the first time we’ve ever seen the freighter Kahana, as well as the Black Rock’s cameo at a private auction. Speaking of which…

    Thanks to the auction scene, we finally have enough pieces of the puzzle to put together for ourselves exactly how the Dharma Initiative wound up on the island. Magnus Hanso owned the Black Rock. A relative of his named Tovard Hanso, somehow found the journal in Madagascar, and through it, learned of the island’s existence and unique properties. In the 20th Century, Alvar Hanso used that information to plant his Dharma Initiative on this very special island. And there you have it. But with the journal holding such crucial information about the island, what could have made the Hanso family decide in 1996 that it was suddenly okay to let that information pass on to someone else, aka the highest bidder? I suspect the downfall of the Dharma Initiative on the island — better known as the Purge — had something to do with it. Perhaps with Hanso’s finances taking a hit from Dharma’s loss, he was forced to sell off his most prized relic to keep himself financially afloat.

    Since the Black Rock set sail in 1845 and subsequently wrecked on the island, this gives us a definitive date for the scene at the beginning of “The Incident,” depicting the beachside meeting between Jacob and his nemesis.

    “The Constant” is the hands-down fan favorite episode of all time and an absolute triumph of storytelling. Desmond’s time-skipping could have been wildly confusing, yet it not only made sense, but the writers never lost the hour’s emotional anchor (the Desmond/Penny relationship) in the face of so much scifi time travel exposition. The coup de grace is the beautifully-executed final scene, when Desmond makes his phone call to Penny. The slick editing in this scene elevated everything, allowing the actors to hit the perfect emotional note, and achieving a new artistic high for the series.