Plot hole: At the Precinct after the second spa incident, Captain Stonetree refers to "two unexplained reflex murders in one night." But the first victim survived the attack - so there was only one murder, not two. A little worse than a simple character mistake, since he's the police captain and knows the case. Schanke gets it right later, when he says, "One murder and one attempted murder." (00:14:20)
Plot hole: In the morgue, Nick tells Nat that vampires disappear when they die. Not so in this series. "Forever Knight's" vampires, defying old movie clichés, remained stubbornly intact when staked, making Nick's statement here a glaring contradiction of canon. (00:16:05)
Continuity mistake: Nick gets a phone call telling him another murder victim has been found and that she's been dead for at least a week. In the very next scene, Schanke says that the victim "disappeared after a date last night." (00:27:00)
Character mistake: Nick asks Janette if she's ever turned anyone else into a vampire - an odd question, considering the fact that he already knows she has. He was there when she brought the baroness across in the 18th Century flashback sequence for "If Looks Could Kill." It's even odder that Janette tells him she's never done it, since she knows that Nick knows she has. Apparently, the only one not in the know here was the scriptwriter.
Continuity mistake: When Nick breaks into the old Chinese herbalist's warehouse, he twists and breaks a doorknob lock. But when he walks through to the inside, there's a latch-and-bar array instead of a knob. It's a completely different door.
Factual error: The supposed ballerina in this episode's flashback to 19th century France is not employing any real ballet steps or arm movements. All she's doing on stage is standing still and waving her arms in the air, performing something that looks rather more like semaphore than ballet. (00:10:10)
Continuity mistake: The wooden plank with which Alexandra impales Nick completely changes angles (from flat side tilted left to flat side tilted right) between the time it strikes him and the time he pulls it out. It also appears to "grow" an inch or so wider than it was before. (00:39:00 - 00:40:25)
Continuity mistake: The tow truck and the red van it's towing change positions at the alley's entrance between shots. (00:01:00 - 00:23:35)
Other mistake: Nick pronounces the plastic surgeon's name as "Yergen" in one scene and as "Jergen" in the next. At the end, she becomes Dr. "Yergen" again. (00:29:40 - 00:31:10)
Factual error: Nick's '62 Cadillac had an attached police radio, but never had a car phone, nor the giant external antenna attachment they required in the early 90s. Yet Schanke somehow makes a call from Nick's "car phone" in this episode.
Answer: Nick was sick and tired of being an immortal bloodsucker. He wanted to be human, fall in love, get married, have children, grow old and die. As for Janette, according to her, she fell in love and the passion she felt "cured" her of her blood lust.