Heart of the Alien is the sequel to the game Out of this World, also known as Another World. The story picks up immediately after the end of the first game. You begin as Lester and his alien friend, "Buddy," land their pterodactyl in the ruins of Buddy's village. Lester was knocked unconscious in their escape, so Buddy lays him down on a cot to rest. The people who used to live in Buddy's village remain enslaved, so he decides to go on a mission to free them. Thus, you control Buddy as he sets off to free the people and find a way to send Lester home. "Heart of the Alien" was only released within the Sega CD bundle containing Parts I and 2.