Exiles of Time
Nelson S. Bond
 After a strange bloodstone amulet is found in an ancient Arabian tomb by archaeologists, the native employees of the expedition attack the others when they refuse to leave. One of the archaeologists, Lance Vidor, seeks refuge in the tomb, where he is transported to a different point in the time circle of Earth. Vidor finds others who have been summoned to the time period for the purpose of saving the Earth from an oncoming comet.