A psychopathic young beachcomber pretends to befriend a mother and two daughters living at their summer home.

Prof. Erling and his financial backer Victor build a prototype time machine to snatch objects from the past. Latest find, a statuette, radiometrically dates to 5200 AD! When this draws colleague Richard Hedges to the island lab, Erling reveals that 20th-century objects put in the machine seem to be "traded" for analogous future objects by intelligent life. And on the sly, Victor's been trying to get a living visitor. Does the future need help, or is the present in danger?