Mr Pilchard is furious. His class came last in the poetry contest, mostly because of Sid's terrible effort. He gives Sid an ultimatum - write the winning entry in the upcoming story competition or be fed to the classroom guinea pig. Sid turns to his sister, Wendy, and his evil-genius neighbour, the Mighty Professor Skeletron, for help. Together, they consult a psychic cat who leads them to the perfect solution - give a Shakespeare story a sci-fi twist. But when their story comes to life and causes an alien invasion, they have to find a way to travel back in time and change the past.