A detective duo hunts a criminal organization, which is using an unknown liquid explosive material.

The reinvigorated elderly group that left Earth comes back to visit their relatives. Will they all decide to go back to the planet where no one grows old, or will they be tempted to remain on Earth?

Two scientists involved in chimpanzee research -- one maintaining that the animals should be kept in their native habitat in Africa without human interference, the other trying to train them in sign language in a domesticated atmosphere -- join forces when they learn that the government plans to cut off the language grant and use the chimps for radiation research.