Millie and Oscar are ordinary children, but it all changes when they are introduced to Mr Wallatt, an eccentric scientist.

Millie, Oscar, and their friend Derek, learn that Mr Wallatt is an eco-warrior and a hoarder, who believes that everything should be recycled so the planet is deeply cherished. He is plotting to help migratory birds on their long seasonal flights by reinforcing the magnetic field at the North Pole using a giant battery and a large electromagnet from his attic. 

In a separate part of the world, in Arizona, Jed Bronzovic, an astronomer, has been given the task of studying the asteroid belt. He finds a large asteroid made mostly of iron that has been diverted and may pass close by the Earth – he calls it Ferrus-11.

As Mr Wallatt, the children and their fast-running cat, Torpedo, make headway with their experiment, Jed calculates that Ferrus-11 is going to collide with the Earth and its impact may lead to complete loss of life on the planet. Warning broadcasts are made around the world, and it soon dawns on the three children that Mr Wallatt's magnet may hold the key to deflecting the asteroid. With time quickly running out, can they complete the mission and save the Earth from destruction?