There had never been anything like Lost on television prior to its premiere in 2004 — and in a way, there hasn’t been anything quite like it since. The story of a group of plane crash survivors on a remote, increasingly mysterious island revolutionized the way people thought about TV. It was the water cooler show to end all water cooler shows for a spell, spawning online forums, columns dedicated just to weekly theories and references, and endless speculation.

Lost tended to put its characters first, driving the story with flashbacks, flash-forwards, and the eventual flash-sideways. By the time Season 4 rolled around, an episode of the show could be anything, and in a time where some viewers thought Lost might be on shaky footing, along comes Episode 5, “The Constant,” celebrating its fifteenth anniversary today (February 28th).

Written by showrunners Carlton Cuse and Damon Lindelof, “The Constant” gave a bolt of energy to the show’s nervous system, reinvigorating it with that balance of sci-fi oddities and high-octane emotional beats that made the show so very addictive in the first place.

For those who haven’t spent time on the island in a while — if you haven’t gone back, so to speak — let us get you back up to speed. The show’s fourth season was the shortest at 14 episodes, which feels like a silly sentence in our present-day reality of entire seasons capped at nine or 10 episodes. (Remember the days of luxurious, weekly sit-downs, knowing you were only halfway through a season that could stretch 23 episodes at a time?)

At this point in the story, our core group of Islanders are aiming to connect with the mysterious freighter, and Desmond (Henry Ian Cusick) and Sayid (Naveen Andrews) are on a helicopter with everyone’s favorite ever-resilient pilot, Frank Lapidus (Jeff Fahey). It’s here, flying through a lightning storm, that our long-haired Scot begins flashing through time and suddenly finds himself in 1994, training in the Royal Regiment of Scotland, feeling as if he just emerged from a dream about an island. The one thing present in both timelines? The perpetual draw to his beloved, Penny (Sonya Walger).

Again, there was so much to love about watching Lost, even beyond the Easter eggs like this episode’s painting of a ship called The Black Rock. Film buffs enjoyed winks to pop culture staples woven throughout the script, and literary and history lovers got their fair share of references, too. Desmond, stranded on the island in a shipwreck after an attempt at sailing around the world, languished in the infamous underground hatch for years, and at this point in the story is reaching the end of his rope: In so many ways, Desmond is an Odysseus figure, mirroring quite a few key points of the protagonist in the Greek epic; the writers even lifted the name of Odysseus’s faithful wife from The Odyssey, Penelope herself.

Lost (ABC)