Mr. Plankton: Plot, Cast, Ending & Where to Watch

Woo Do-hwan

Woo, best known to international audiences from The King: Eternal Monarch and Bloodhounds, anchors Mr. Plankton as Hae-jo and is on screen for almost every scene. The role asks him to carry both registers the script alternates between: the loose, self-deprecating comic energy of the road-trip episodes, and the harder, quieter physical work of playing a young man whose body is failing under him without letting the show tip into sentimentality.

Lee You-mi

Lee — the Squid Game and All of Us Are Dead actress who broke into international audiences in 2021 — plays Jae-mi as the script's stealth protagonist: not the loud half of the central couple, but the half whose interior life the series is actually tracking. Her arc is the question of how a young woman raised to want what her wedding paperwork promises arrives at the realisation that she would rather be on a Mongolian road with an ex than at her own ceremony.

Oh Jung-se

Oh, the It's Okay to Not Be Okay character actor who has spent the past decade specialising in finely-tuned emotional supporting parts, plays Eo-heung as the abandoned fiancé pursuing Jae-mi across the show's road map. The role is calibrated to refuse the genre's instinct to read him as either a slapstick punching bag or a clean villain — Eo-heung is a man who has been publicly humiliated at his own wedding venue, and Oh plays the pursuit as grief rather than rage.

Kim Hae-sook

Kim is one of South Korean television's most-decorated senior performers, with a career that runs from Thirst to Coin Locker Girl to the Decision to Leave ensemble. In Mr. Plankton she plays Beom Ho-ja, the elderly woman whose private archive of artificial-insemination records contains the answer to Hae-jo's paternity question. The performance is the show's stillness register: the figure the road trip is moving toward, and the figure who finally tells Hae-jo the truth about the family he never had.