An Evil Immortal, Kuyler, has hired himself out down through time as an assassin -- the most successful killer in all of history. He strikes again in modern day Paris using his signature disguise as a mime. A French Police Detective, LeBrun, suspects that Duncan MacLeod is connected to Kuyler, but of course he cannot imagine that Kuyler once killed an eighteenth-century baron under MacLeod's protection. When LeBrun is wounded protecting Tessa from Kuyler's men, MacLeod confronts the Immortal assassin and puts an end to his centuries-old reign of terror.

MacLeod stumbles across the trail of an Immortal, Xavier St. Cloud, who has lived in hedonistic splendor down through the ages by remorseless robbing and killing innocent men and women. MacLeod had nearly fallen victim to this remorseless killer behind the front lines during World War One, when Xavier used poison gas to loot a payroll truck. He uses even deadlier gas in modern day Paris, and MacLeod must track him down before he kills again. He succeeds in defeating Xavier, but the Evil Immortal escapes with his head. In a humorous yet touching subplot, Richie falls for a glamorous older woman, not realizing she is married, and Tessa must disentangle him from the woman's clutches.

Grace Chandel has been a Good Immortal, working for the betterment of mankind as a midwife, doctor, and scientist over the centuries. Her one weakness is another Immortal, Carlo Sendaro, a former lover who is obsessed with her and refuses to let her go. He slays Grace's current (mortal) lover and, when she refuses to run off with him, frames her for the killing. She turns to her old friend Duncan MacLeod for help.