A night spent playing war games with Darius forces Duncan MacLeod to conclude that his friend may be a priest, but he still thinks like a warrior. Their game comes to an unexpected end as dawn breaks with the arrival of Grace Chandel, disheveled and tired. Grace, an Immortal known to both Duncan and Darius, tells them that her mortal lover has been murdered and their laboratory burnt. With an Immortal’s instinctive aversion to officialdom, Grace has avoided the police. Darius offers to let Grace stay in the rectory or to find her sanctuary in a convent, but it is agreed that she will stay with Duncan on the barge. She tells Duncan that her lover was growing frustrated with aging and that she stayed away, as a handsome Immortal friend would only have made things worse. She asks Duncan if Tessa will mind her staying on the barge and he assures her that she won’t.
When Tessa comes home to find another woman in the bathroom, Duncan isn’t so convinced that he was right. He tells her and Richie that he has known Grace since the late 17th century, when he found her acting as a midwife. She was too tired to fight and offered him her head, but he declined and they had been friends ever since. He met her again later, in Paris in the middle of the 19th century, when she left France to journey to the Amazon with Carlo Sendaro, another Immortal, but she left Sendaro when he began demanding that the natives worship him. Sendaro had never forgiven this and had pursued her ever since, convinced that she still loved him and determined to take her back to his plantation.
When Grace emerges from the bathroom, Tessa cannot find it in her heart to be angry when she sees the fear and uncertainty on the Immortal woman’s face. Whilst she finds Grace some clothes, Duncan goes up on deck to work on the barge. Grace joins him and tells him that Tessa is well suited to him, a mortal with an old soul. Tessa suggests that Grace would feel better in some of her own clothes and Duncan agrees to go to her apartment. When he gets there, he walks into Inspector LeBrun coming out. The police have found the gun used to kill Paul Warren, Grace’s lover, in her apartment, after an anonymous tip-off. Duncan goes back to the barge to tell Grace, but LeBrun arrives hot on his heels.
While Duncan distracts LeBrun, Tessa and Grace make off in the speedboat. As they reach the chapel, Grace feels an Immortal nearby and they see Carlo Sendaro blocking their path. Darius comes out, feeling their presence. Whilst Grace and Sendaro go into the chapel, Darius and Tessa wait outside. Duncan arrives, having lost LeBrun, and goes inside to confront Sendaro, who is so consumed with jealousy that he wants to fight MacLeod on Holy Ground. Carlo admits that he murdered Paul Warren, planted the gun and tipped off the police. Enraged, Grace tells him to get out.
While Richie and Duncan go to work finding a new identity and a new passport for Grace, using the name of an infant who died after 8 days of life, Tessa and Grace go to Paul Warren’s grave. Tessa is uncertain how to deal with Grace, knowing that she is one of Duncan’s former lovers. Grace tells her it is past and asks her not to hold it against her. Tessa finds that she cannot. Grace senses an Immortal nearby and, once again, sees Carlo Sendaro. When Tessa gets back to the barge, she tells Duncan that Grace agreed to go with him to protect her. Duncan goes to Sendaro’s home and the two fight, until they are stopped by Grace, who leaves with Duncan.
Grace will not let Duncan take her to the airport, but goes to see Darius before she leaves. As she comes out of the chapel, she is arrested by the police, but Sendaro overpowers them. Grace runs, straight into the arms of LeBrun, who handcuffs her. When Sendaro tries to interfere, LeBrun shoots him, but is surprised when Sendaro gets right back up and keeps coming. With LeBrun down, Carlo cuts the handcuffs and leaves with Grace. Darius rings Duncan to tell him and MacLeod heads straight for Sendaro’s home, followed by the police. Sendaro flees on foot with Grace, pursued by Duncan. They run into a Métro station and into the tunnels. Duncan catches them up and fights with Sendaro, who traps Duncan’s foot in the points. As Duncan struggles to free himself, Sendaro comes for the kill. Desperate, MacLeod throws his jacket, which Sendaro shrugs aside. As he does, his sword touches the power line and he is electrocuted. Duncan frees himself, but Sendaro is not so lucky. Before he can recover from the electrocution, a train decapitates him. After the Quickening, Duncan and Grace make their escape from the tunnels and, later, say their goodbyes on the quay before she leaves.