When fatal stabbing fails to kill him, Alfred Cahill becomes convinced that he has been chosen by a higher power to wage a crusade against 'perversion', and cuts a bloody path through Paris, murdering prostitutes and pimps, and endangering an old friend of Tessa's who has become a call girl. MacLeod tries to explain Immortality to Cahill, but he can't get through to him, and finally is forced to take his head.

MacLeod's old compatriot Hugh Fitzcairn comes to town bearing a mystery -- some of their other Immortal friends have disappeared suspiciously. MacLeod realizes that someone may be following Fitz, and realizes too late that Fitz has put Darius in danger by visiting him. Finding Darius dead in his chapel and Fitzcairn kidnaped, MacLeod won't rest until he finds the men responsible. Tracking the killers of his old friend, MacLeod discovers that there is a band of mortals hunting Immortals, and even holy ground is no protection from them. MacLeod finds the renegades in time to save Fitzcairn and confront James Horton, leader of the Hunters, but Horton eludes his grasp.

A mortal named Pallin Wolf, one of the renegade Watchers who believes the Immortals must be eliminated, lures an Immortal to his house and kills him, getting the advantage by tricking him into a sealed room that is completely dark, then stalking him with night vision goggles. Meanwhile, a Gypsy fortuneteller they meet in a restaurant, Greta, warns Tessa that she is in danger. When Tessa is kidnapped by Wolf, MacLeod returns to Greta, asking for her help. But she's mostly a hustler, and not accustomed to getting actual visions, so the clues she is able to provide are meager. Finally, Mac finds Wolf's house, where Wolf is waiting for him. He meets Wolf in the dark room and all seems hopeless until he remembers a matchbook Greta gave him with her phone number in it. Lighting the matches, he regains the advantage and kills Wolf. However, as Tessa and Richie are heading for the car, a young junkie accosts them for money, and in an act of senseless violence, shoots them both. As Mac mourns,

When her mentor Rebecca is killed, Amanda is determined to avenge the death, even though it means going up against the formidable Immortal Luther, and very possibly losing her head. She comes to Mac for a final fling before her likely death, and when he discovers that she's after Luther, he tries to take the battle on himself, feeling he has a better chance of survival. Together they discover that Luther is hunting the pieces of an ancient crystal that Rebecca divided among her students, believing that the whole crystal will make him invulnerable and ensure that he is the Last Immortal. In the final confrontation, both Amanda and MacLeod take their turns battling the ascetic Luther.

Pete Wilder just saved Richie from an attack by some guys wearing Watcher tattoos. Or did he? Nothing is what it seems, and MacLeod becomes increasingly wary of Pete, despite Richie's protests that the guy is his friend. When MacLeod's mistrust gets the possibly innocent Pete killed, Mac becomes increasingly unsure of himself. Unknown to MacLeod, his old enemy Horton is pulling all the strings. Horton is secretly training escaped killer Lisa Halle to go after MacLeod while he's troubled and vulnerable.

Lawyer Robert Waverly is leaving his mistress' apartment with his video camera when he sees MacLeod locked in combat with an evil Immortal. Waverly makes sure he gets it all on tape -- the fight, the death, the Quickening. He then tries to cut a deal with MacLeod: if MacLeod kills Waverly's wife, then Waverly won't go to the police. When Kurlow, partner of the Immortal MacLeod killed on the tape, comes after MacLeod, Waverly, unaware of what he's dealing with, proposes another deal. A la ""Strangers on a Train,"" Waverly will kill Kurlow and MacLeod will kill Bruno's wife, and no one will suspect a thing. Waverly challenges Kurlow, who kills Waverly easily and MacLeod is left to save Waverly's wife and get rid of Kurlow.

Recent Immortal Michael Christian has been on an incredible string of luck, taking a number of heads from unarmed and vulnerable opponents, including May-Ling Shen, who taught MacLeod the martial arts in 1780's Mongolia. Christian's Watcher, Rita Luce, has been doing more than just watching, supplying Christian with classified information on the other Immortals and their weaknesses. MacLeod, unaware of Christian, goes on a vision quest to his cabin on Holy Ground -- deliberately leaving his sword behind. The race is on for Joe Dawson to figure out Rita's secret before Christian sets his sights on MacLeod.

In the 1600s, MacLeod sought refuge for a time in a monastery founded by Paul, another Immortal. There he encountered Kalas, an Immortal monk with a heavenly singing voice. When MacLeod discovered that Kalas was routinely taking the heads of Immortals as they left the sanctuary, MacLeod and Paul expelled Kalas from the monastery, separating him from the music that was his life. Now in the present, Paul and his choir have been lured out of their monastery for a concert tour. When Paul disappears after a concert, MacLeod discovers that Kalas is after his revenge. Meanwhile, two mysterious deaths at the hospital seem to be linked to negligence on Anne's part. Later, when drugs are found in Joe's bar, it becomes obvious that Kalas is trying to destroy MacLeod's friends before coming for him. MacLeod confronts Kalas and finds that Kalas is a strong and skillful fighter, better than MacLeod has faced before, and is nearly the victor. To save himself, MacLeod throws himself off the concert ha

MacLeod is picked up at the airport in France by his old friend, Hugh Fitzcairn. For the first time in the 350 years MacLeod has known him. Fitz has settled down as a Universitv Professor with the love of his life, Naomi. Flashbacks show MacLeod and Fitz's first meeting, when MacLeod was protecting the Doge's daughter from Fitz's amourous advances in Venice, 1637. When Naomi's jealous ex-lover is found strangled next to a computer displaying Fitz's falsified teaching credentials, Fitz goes on the run from the police. MacLeod realizes that Fitz is being framed by Kalas, who has followed him from the U.S. Kalas challenges Fitz and takes his head while MacLeod watches, unable to interfere.

When Immortal Ceirdwyn and her mortal husband are gunned down by a street gang, she calls upon her skills as an ancient Celtic warrior to exact her revenge on the members of the gang, one by one. At the racetrack watching Richie's success at racing, MacLeod befriends a young pickpocket, the brother of one of the gang members, and learns of the killings. MacLeod, who has known Ceirdwyn since before they helped smuggle Bonnie Prince Charlie out of Scotland in 1746, feels he must stop Ceirdwyn and make her see that revenge is not the answer -- a lesson she helped MacLeod learn in the bloody aftermath of Culloden. In return, Ceirdwyn helps MacLeod see that, although loving a mortal can be dangerous for the mortal, it is the mortal who must choose whether to take the risk. MacLeod calls Anne. Meanwhile, Richie ""dies"" in a firey crash during a race, a crash that also takes the life of the champion, Basil.

Nearly 350 years ago, MacLeod was the devoted lover of Kristin Gilles, a beautiful Immortal who taught him to be a gentleman. When he found another love, Kristin refused to let him go, killing his new lover. Now Kristin is sharing her bed with another new Immortal full of potential -- Richie. Methos, who knows MacLeod has never been able to kill Kristin because of his strict code of honor, has arrived in town to watch the fireworks as MacLeod tries to convince Richie that his new-found love is dangerous.

ER trauma surgeon Anne Lindsey responds to the call for help after an explosion devastates a subway station, but when a subsequent explosion rocks the station, Anne is trapped. MacLeod remembers WWII London where he and the woman he loved, reporter Diane Terrin, were trapped in a bombed air-raid shelter during the Blitz, running out of time and air. MacLeod is desperate to rescue Anne before he loses her like he lost Diane.

In 1755, MacLeod made a promise in order to save the life of a young friend. It comes back to haunt him when Kassim, the Immortal to whom he made the promise, demands that MacLeod assassinate the tyrannical dictator of a small Middle Eastern country. When his refusal gets a good man killed and puts Rachel's life in jeopardy, MacLeod is torn between doing what he believes is right and keeping his promise.

After the Scottish massacre at the Battle of Culloden in 1746, Duncan MacLeod was a man possessed, obsessed, with killing the English bastards who had destroyed his people. Now Immortal Steven Keane has come to make MacLeod pay for his murderous crimes. Amanda urges MacLeod to take Keane's head and be done with it, but in his heart MacLeod knows that Keane is right -- he is a murderer -- and that Keane is judging him just like MacLeod has judged so many others.