When a street gang guns down Immortal Ceirdwyn and her mortal husband, she calls upon her skills as an ancient Celtic warrior to exact her revenge on the gang members, 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 fiery crash during a race, a collision that also takes the life of the champion, Basil.

In the 1600s, MacLeod sought refuge in a monastery founded by Paul, another Immortal. There, he encountered Kalas, an Immortal monk with a heavenly singing voice. When it was discovered that Kalas was routinely taking the heads of Immortals as they left the sanctuary, he was expelled from the monastery and the music that was his life. Paul and his choir have been lured out of their monastery for a concert tour, and MacLeod discovers that Kalas is after revenge. Meanwhile, mysterious deaths at the hospital seem linked to negligence on Anne's part. It becomes evident that Kalas is trying to destroy MacLeod's friends before coming for him.

When a religious leader, John Kirin, dies on Anne's operating table and then returns from the dead, his believers know a miracle has occurred. MacLeod knows better. He watched as Kirin, then known as Kage, massacred POWs in the Spanish Civil War and left a band of Cambodian refugee children to die at the hands of the Khmer Rouge. Kirin swears that experience changed him forever, turning him from a man of war to a man of peace. When a tabloid reporter trying to get the goods on Kirin winds up dead in MacLeod's dojo, MacLeod is certain Kirin is responsible. Kirin protests his innocence and realizes the real killer is Matthew, one of his faithful disciples trying to protect him. Kirin confronts a disillusioned Matthew, who manages to kill Kirin before dying himself in a rain of police bullets. In the Tag, Kirin and MacLeod have made peace as Kirin takes to the road, hoping to do good elsewhere.

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.

To save his own hide, petty hoodlum Benny Carbassa, the Nathan Detroit of Immortality, turns MacLeod over to an aging gangster determined to see MacLeod dead before he dies. In the midst of this, Anne returns, having convinced herself that MacLeod will open up in his own time and determined not to push him too hard. In flashback, we see MacLeod's first meeting with Benny, in 1938 at the Coconut Lounge, a club operated by two young brothers who are rivals for the same torch singer.

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.

MacLeod is tormented by visions of his own death, beheaded by a mysterious dark-hooded figure. Anne tries to convince him to seek medical help, but instead he turns to his old friend Garrick, who has spent centuries studying the mind. MacLeod saw Garrick in the 17th Century, when MacLeod barely escaped being burned as a witch. What MacLeod didn't know was that Garrick was not able to escape as well. Garrick convinces MacLeod that the dark-hooded figure is a racial memory that haunts all Immortals and that the way to defeat it is to not fight it, to accept it for what it is. When MacLeod, haggard and exhausted, faces the specter for the last time, puts down his sword and refuses to fight it, the figure goes for MacLeod's head -- until at the last moment MacLeod realizes the figure is Garrick, seeking his revenge after all these years. In the Tag, Anne, frustrated that MacLeod won't open up to her despite their intimate relationship, leaves him.

Immortal David Keogh, once an indentured servant, is a noted craftsman with his heart set on marrying his sweetheart, Jill. Unfortunately, Jill does not agree. Although she loved Keogh once, she was unable to handle it when he confided the secret of his Immortality. Now Keogh won't leave her alone and she's coming to MacLeod, whom Keogh respects and might listen to, for help. But Keogh won't listen, convinced that Jill needs him as much as he needs her. In flashback, we see a time in MacLeod's life when he, too, was obsessed with a woman he couldn't have. When Jill is killed in a tragic accident while trying to get way from Keogh, Keogh blames MacLeod and swears vengence.

What happens to a kid who hits Immortality before he hits puberty? MacLeod and Richie take in 10-year-old Kenny, who asks for their protection after the fatherly Immortal who was protecting him is beheaded. Kenny, we discover, is not the sweet little lamb he appears to be. He has been Immortal for nearly 800 years, and has survived all that time by convincing other Immortals to take him in and protect him -- and then taking their heads. Kenny tries to get MacLeod, but he is continuously thwarted by the presence of Anne. Kenny attempts to get Anne out of his way, but MacLeod, realizing the truth about Kenny, manages to rescue her. He goes after Kenny to stop him from killing again, but Kenny manages to escape by blending in with a group of innocent children.