Howard Chase accepts the opportunity to leave Earth forever offered by aliens, but he eventually becomes homesick. The aliens insist he keep his part of the bargain until he saves the life of one of them.
A bomb meant for another planet will destroy Earth in 12 days unless someone finds a way to deactivate it. Though scientists are stumped a boy's dog whistle proves just the thing.
People are able to barter for amazing scientific marvels at an odd little shop, but only for a brief time, as the proprietor is only collecting Earth objects for his space fair for a limited time.
Astronomer Bradley Wells is abducted by the alien Sardor who has captured and shrunk several planets to extract their elemental resources. But Wells traps Sardor, returns the planets to their proper sizes and positions, and returns to Earth.