The Keeper is an alien who travels the galaxy collecting living pairs of interesting or rare animals. His courtly overtures towards the Robinsons belie his true intention -- to add a pair of humans to his incredible menagerie.

Will becomes fast friends with Captain Alonzo P. Tucker, an Earthling who escaped his alien captors to become a wandering space buccaneer. But Tucker's roguish charm hides a secret that could destroy them all.