Troubles with The Keeper would be over if Dr. Smith hadn't skulked aboard his ship and released all the animals, putting The Keeper in a position to blackmail the Robinsons for their children.
Dr. Smith tries to steal the Keeper's spaceship, but succeeds only in releasing his collection of animals, many of them dangerous. Although The Keeper can easily recall his creatures, he refuses to do so unless the Robinsons give him Penny and Will.—Mister-UHF