Carbon dioxide is out of control on Earth, and the fate of humankind rests in the paws of four experimental, untested Animal Astronauts (AlphaWolf, SmartHawk, LaserShark, and StinkBug) who are seeking another habitable planet; first destination is the Plant Planet which at first looks perfect, except that the abundant plant life can think for itself--and it thinks that it really does not like the AstroNuts.

Zak Nine and Erro believe they've finally found a way to get off planet Alcatraz. Together with their new partner, the boys board a small spacecraft and fly off the planet, past the metal moon, and head into space, but when the stars begin to look strange, Zak and Erro realize that something is very wrong. What will happen when the boys learn Planet Alcatraz's biggest secret, and will they ever get to return home?

Pursued by a killer cyborg tank and surrounded by snakes that spit fire, teenage friends Zak and Erro the furling from the planet Quom, must figure out a way to survive if they are ever to escape from the prison planet called Alcatraz--a situation they are in because they stowed away on a space ship they did not know was headed here.