An immortal named Grayson is targeting the friends and disciples of his old friend Darius, an immortal who was once a great warrior but is now a Catholic priest. Darius sends Duncan a message warning him of Grayson's treachery, and Duncan must protect Grayson's next target.
An immortal thief named Xavier St. Cloud visits Darius and confesses his crimes to him after a robbery during which he murdered six people. According to the laws of the Catholic Church, Darius cannot reveal to the police what he learned during St. Cloud's confession. Duncan, who suspects that St. Cloud was responsible for the crime, then takes it upon himself to find him.
During a rehearsal, the manager of a band is thrown from a balcony and killed while having an argument with the band's lead singer. Duncan, who is there with Tessa and Richie as guests of the backup singer, believes the manager was killed by a mentally handicapped immortal he once befriended.
Grace, an Immortal who has focused on healing rather than fighting, is framed for the murder of her mortal husband by an obsessed ex-lover, the Immortal Carlo Seandaro. Duncan must step in to protect her from her own weakness.
Amanda, an immortal thief and former lover of Duncan, is confronted by the immortal Zachary Blaine, her former partner in crime. She convinces him not to kill her in return for providing him with the chance to take Duncan's head.
Gabriel Piton, an immortal fashion designer, kills one of his models after she finds a stash of stolen artifacts in his apartment. Now the girl's roommate, who is an acquaintance of Richie's, is in danger of the same fate, and Duncan, who is an old friend of Piton's, must step in to prevent his friend from killing another innocent person.
Mark Rothwood, the son of diplomat Allan Rothwood, rapes the step-daughter of the immortal Colonel Bellian. Duncan, Tessa, and Richie go to the Rothwoods' house to visit Allan, who is an old friend of Tessa's, and Bellian shows up for revenge. Believing that Rothwood deserves a fair trial, Duncan must guard the house against the siege of Bellian and his team of mercenaries.
Duncan receives a visit from an old friend, the immortal Hugh Fitzcairn. Fitzcairn informs him that several immortals have gone missing recently, and that he thinks something isn't right. When Darius is killed in his church they know that it isn't the work of another immortal, so they vow to avenge Darius by finding who is responsible.
The presentation episode for "THE WATCHERS"; a mysterious society of individuals dedicated to watch and write down information about immortals (like Duncan) ,in theory, without ever bothering any of them or interfering.
Duncan, Tessa, and Richie attend a photographic exhibit featuring Immortal Gregor, and Duncan discovers that the other exhibitor is someone he loved decades earlier, who had sent him away in order to focus on her work. She recognizes him, but he doesn't know how to tell her that he is the same man she loved. Meanwhile, Gregor appears to have changed since Duncan knew him, as he appears to have become disillusioned and can no longer feel emotion.
Duncan takes on Charlie DeSalvo to prove he's good enough at martial arts to work out at the dojo. Dawson tells Duncan that Quenten Barnes is free and killing mortals, but Duncan refuses to get involved. Then Duncan's old friend Michael Moore turns up, determined to take Barnes' head. In flashback, Michael was unable to save his mortal girlfriend Jeanette. Barnes beats Duncan to the priest who attended his execution, as Duncan tries frantically to prevent more killings.
When Richie interferes with Immortal Annie Devlin and her IRA gang, she vows revenge. Meanwhile, Duncan starts teaching Richie. In flashback, Duncan rescues Annie from a massacre but refuses to help her crusade.
Amanda shows up at the dojo with a suspicious offer of friendship. Then Duncan helps Amanda escape from two attackers that she insists she doesn't know. In flashback to 1930s Germany, Duncan is trying to help a scientist escape when Amanda attaches herself to him to get away from police chasing her. In modern day, Duncan tells Amanda about the Watchers but they discover the men chasing her are FBI.
Duncan allows the dojo to be used for a karate movie starring Jimmy, a former student of Charlie's. When one of the stunt men is poisoned, Duncan and Charlie think someone may be trying to kill Jimmy and suspect the Tong are involved.
Duncan saved Immortal Carl Robinson from lynching in 1926 Louisiana. Carl became a famous colored league baseball star with aspirations of becoming a politician, but he has since become disillusioned after seeing years of racism and corruption. He now lives on the streets and steals to get by. When he steals Charlie's car to get away from drug dealers after stealing their money, Duncan tries to help him overcome his longstanding hatred of and distrust for whites, and he helps him deal with a racist cop who is after him.
Immortal Anthony Galen attacks Duncan in a deserted amusement park. Losing, he tries to escape and hits mortal Tommy Bannon with his car, killing him. Duncan feels guilty over Tommy's death and tries to console his mother. In flashback, the fiancé of Duncan's current bed partner challenges him to a duel, but accidentally stabs the girl instead. Tommy's mother asks Duncan if Tommy's death was really an accident, telling him that Tommy was an investigative reporter and he had been scared of something. Duncan decides to find the connection between Tommy and Galen.