Starring Peter Davison as the fifth Doctor. A new adventure in time and space for the Fifth Doctor and his companions Tegan, Turlough, and Nyssa. Eight slash Q Panenka, a craggy comet, has an elliptical orbit that takes it between Earth and Jupiter. Which, in the 24th-century, makes it a cheap means of space freight, the second class postal service of the solar system. But when the TARDIS lands on Panenka, the Doctor, Tegan, Turlough, and Nyssa discover a community plagued by thefts and mysterious disappearances among the "piggybackers" who eke out a desperate existence on the comet.