Chronicle X has two main game modes: the Narrative Mode, where players play a scripted campaign, and Conquest Mode where the alien player aims to conquer the Earth, and the human players aim to prevent that.
The original form of the game has one player playing the alien side (Overmind Player), and one or more players playing the human side (Hero Players). However, an Expansion adds a Co-Operative Mode where a deck of cards control the alien side.