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.

Father Bernard has a secret he thought he'd buried 50 years ago at the bottom of the Seine. When Ernest Daimler, the Nazi Major who Bernard killed as a young boy and threw in the river, appears at his church looking not a day older than the day he died, Father Bernard realizes he's like MacLeod. As a child, Bernard watched MacLeod die and revive during a mission for the French Resistance and MacLeod swore him to secrecy. Bernard goes to MacLeod for help. Meanwhile, Anne tells MacLeod that she is pregnant -- by an old friend she sought for comfort after MacLeod's ""death."" MacLeod tries to adjust to the concept of being a father. When Daimler kills Father Bernard and comes after Anne, MacLeod kills Daimler and Anne witnesses what being part of MacLeod's life really means. Unable to deal with the part of herself that wanted to see Daimler die, Anne leaves MacLeod.