Ask any fan of Lost what the absolute peak of the series was, and they aren't going to tell you about the smoke monster or the polar bears. They’re going to talk about a phone call. Specifically, a phone call between a scruffy Scotsman and the love of his life. Lost season 4 episode 5, titled "The Constant," is widely regarded not just as the best episode of the show, but as a masterclass in how to handle high-concept science fiction without losing the human heart at the center of it.
It's weird.
The episode originally aired on February 28, 2008. At the time, the show was dealing with the fallout of the writer's strike and a shifting narrative that moved from "how do we get off this island" to "when are we in time?" This specific hour of television changed everything. It introduced the concept of time travel—not through a metal box or a DeLorean—but through consciousness itself.
What actually happens in Lost season 4 episode 5?
Desmond Hume is stuck. Physically, he’s on a helicopter heading toward an offshore freighter called the Kahana. Mentally? He’s jumping back and forth between 2004 and 1996. This isn't your standard "flashback" that the show used for three seasons. This is Desmond’s consciousness literally unmooring from the present.
The stakes are surprisingly high for a guy just sitting in a chair. If Desmond can’t find a way to ground his mind in both time periods, his brain is basically going to short-circuit. He’ll die. The show calls this "becoming unstuck," and it’s a terrifying premise because it’s so internal. There’s no villain to punch. There’s just a man losing his grip on who and where he is.
Daniel Faraday, the twitchy physicist played by Jeremy Davies, becomes the MVP here. He explains that Desmond needs a "Constant." This is someone or something that exists in both 1996 and 2004—a familiar touchstone that can anchor his mind. For Desmond, that’s Penny Widmore.
The Physics of the Heart
Faraday’s rules for time travel in Lost are actually pretty rigid, which is why "The Constant" works so well. It follows a logic.
"If anything goes wrong, Desmond Hume will be my constant."
That line, written by Faraday in his journal in 1996, is a massive "aha!" moment. It proves that the future can influence the past, but only in ways that have already happened. It’s a closed loop. Most people get confused by the "flash-sideways" in later seasons, but the time mechanics in Lost season 4 episode 5 are remarkably tight.
✨ Don't miss: Why the Cast of Hold Your Breath 2024 Makes This Dust Bowl Horror Actually Work
Desmond has to track down Penny in 1996—a version of her that currently hates him because he just broke up with her to go join the army. He has to convince her to give him her phone number and, more importantly, to actually pick up the phone eight years in the future on Christmas Eve.
It’s desperate. It’s messy. It’s incredibly romantic.
Why "The Constant" redefined the show
Before this episode, Lost was a character drama with some spooky island stuff. After this, it was a full-blown hard sci-fi epic. Writer Carlton Cuse and Damon Lindelof took a massive gamble. They bet that the audience would follow a complex plot involving Minkowski space and brain hemorrhages as long as the emotional payoff was there.
They were right.
The episode works because it treats the sci-fi elements as a hurdle for the characters, not the point of the story. We care about the "displacement" because we don't want Desmond to forget Penny. We don't want him to die alone on a freighter in the middle of the ocean while his 1996 self is wandering around a military barracks confused.
Honestly, the acting from Henry Ian Cusick is what carries it. He manages to look genuinely terrified. You see the physical toll the time jumping takes on him. When he finally gets through to Penny on that freighter phone, and the music by Michael Giacchino swells? It’s arguably the most earned emotional moment in the entire six-season run.
Breaking down the 1996 vs. 2004 timeline
In 1996, Desmond is a soldier. He’s struggling with his identity and his relationship with Charles Widmore. This is where he meets Faraday at Oxford. This scene is crucial. It’s the first time we see the "lab rat" experiment with Eloise (the rat, not the woman... well, both).
In 2004, Desmond is on the Kahana. He meets Sayid and the communications officer, George Minkowski. Minkowski is the "ghost of Christmas future" here—he’s what happens when you don't find your constant. He’s bleeding from the nose and eventually dies because his mind couldn't handle the jump.
🔗 Read more: Is Steven Weber Leaving Chicago Med? What Really Happened With Dean Archer
The pacing is frantic. The episode cuts back and forth with increasing speed as Desmond’s condition worsens.
Common Misconceptions about Season 4 Episode 5
A lot of people think this episode started the "it was all a dream" or "they were dead the whole time" rumors.
Wrong.
"The Constant" is firmly rooted in the physical reality of the show. Everything that happens in 1996 in this episode actually happened in the past. Desmond isn't changing the past; he's fulfilling it. He always visited Faraday at Oxford. Faraday always wrote that note in his journal. The show is very clear: "Whatever happened, happened."
Another misconception is that Penny was somehow "on the island" or involved in the Dharma Initiative. She wasn't. She was just a woman with a lot of money and a broken heart who spent years looking for her boyfriend. Her role as the "Constant" isn't because of any special powers. It's because of her connection to Desmond.
The technical brilliance of the production
Director Jack Bender did something special here. The visual cues between 1996 and 2004 are subtle but effective. The lighting in the past is warmer, almost nostalgic, despite Desmond's distress. The freighter in 2004 is cold, metallic, and claustrophobic.
The editing is what really makes it. The transitions between the two eras are triggered by sensory inputs—a sound, a touch, a flash of light. It makes the viewer feel as disoriented as Desmond is.
And we have to talk about the phone call.
💡 You might also like: Is Heroes and Villains Legit? What You Need to Know Before Buying
The scene was filmed with the two actors actually on the phone with each other in separate locations to keep the emotion raw. Henry Ian Cusick was on the freighter set, and Sonya Walger (Penny) was elsewhere. That's why the dialogue feels so natural. The "I love you" isn't a scripted Hollywood moment; it feels like a frantic, last-second gasp for air.
Key Facts and Details
- The Number: Penny’s phone number is 0151 773 0532. Fans have tried calling it for years.
- The Book: The episode references Slaughterhouse-Five by Kurt Vonnegut, where the protagonist, Billy Pilgrim, becomes "unstuck in time."
- The Ratings: It was one of the highest-rated episodes of the season and is currently one of the top-rated TV episodes of all time on IMDb.
- The Music: The track "The Constant" is one of Michael Giacchino's most famous compositions, featuring a repetitive, ticking-clock motif that mirrors the urgency of the plot.
The long-term impact on the Lost legacy
Without Lost season 4 episode 5, the final two seasons wouldn't have worked. It gave the writers the "rules" they needed to explore the island's history. It also set the bar for how the show would handle its series finale.
People complain about the ending of Lost, saying it didn't answer enough questions. But "The Constant" proves that questions aren't why we watched. We watched for the people. We didn't need to know the exact scientific formula for how the freighter's proximity to the island caused temporal displacement. We just needed to know that Desmond made it back to Penny.
It's a reminder that the best stories use "the weird" to explain "the human."
Actionable Insights for your rewatch
If you’re going back to watch this episode again (which you should), keep an eye on a few things you might have missed:
- Watch Faraday’s hands. In 1996, he’s much more sure of himself. In 2004, he’s already starting to lose his own memory, which adds a tragic layer to his help.
- Listen to the background noise. On the freighter, the humming of the ship is constant. In 1996, the world is much quieter.
- Check the dates. The 1996 scenes happen around the time Desmond is discharged from the Royal Scots. His uniform details are surprisingly accurate.
- Pay attention to Sayid. He’s the anchor in the 2004 timeline. Without his calm logic and ability to fix the radio, Desmond would have never made that call.
"The Constant" isn't just a great episode of Lost. It's a reminder of why we fell in love with long-form television in the first place. It’s complex, it’s emotional, and it stays with you long after the screen goes black.
Next Steps for Fans:
- Compare the time travel rules in this episode with the "Flash-Sideways" in Season 6 to see how the "Constant" concept evolved into the "Awakening" concept.
- Look up the "Lost Experience" ARG (Alternate Reality Game) details that explain more about the Kahana and its crew, which provides context for Minkowski’s role.
- Re-watch the Season 2 finale to see the first time we see the polar monitoring station that eventually detects the island, which is what allows Penny to be there for the call.