Complex sentence: The Doctor hypnotises Chloe and finds that she is possessed by an immature Isolus, an alien life-form used to travelling through space with a family of millions, which has crashed its pod to Earth due to a solar flare.
Split into simpler sentences: The Doctor hypnotises Chloe and finds out that she is possessed by an immature Isolus, an alien life-form that travels through space with a family of millions. This particular Isolus crashed its pod to Earth due to a solar flare.