The series is about an elite group that specializes in intelligence. In addition to Hill (first season) and Graves (second and following seasons), the other group members were played by Martin Landau (Rollin Hand, expert in disguise), Barbara Bain (seductress Cinnamon Carter, the bait to lure rivals), Greg Morris (Barney Collier, electronics expert), and Peter Lupus (Willy Armitage, the strong man). Landau and Bain left after the third season. In the fourth season, Leonard Nimoy joined the cast as Paris. Later cast members included Lee Meriwether (who guest-starred in 8 episodes as Tracey), Lesley Ann Warren as Dana Lambert, and Sam Elliott as Doug Robert. The last episode aired March 30, 1973.