该剧改编自日本漫画家岩明均的漫画作品《寄生兽》，讲述寄生兽入侵韩国，企图用人类作为宿主来扩大自己的力量，而一支名为“灰色部队”的团队努力阻止寄生兽的入侵。
Scott’s life is in freefall: his girlfriend has just left him, he’s dropped out of studying medicine and he’s desperate for cash to help save his brother. Out of the blue his terminally ill neighbour comes to him for a favour – to help him commit suicide. Scott reluctantly agrees, and in the process, he and his two friends decide to set up their own illicit assisted-suicide bus...
