Forever Knight (1992)

Season 2: Episode 24

Serena, a victim of Nick's immortal bite from the past, has a plan to regain her mortality. According to ancient legend, a vampire will become mortal if she bears a mortal's child. But to conceive, the mortal must possess an extra chromosome and will be murdered soon after conception. When Trilling, who possesses the magic chromosome, is arrested for murder, Serena provides an alibi to get him out of jail. Fully aware of Serena's plan, Nick struggles to solve the murder -- torn between reconciling the wrong he did Serena and preventing yet another murder. But his actions, along with the reasons behind them can never be revealed.