Continuity mistake: The blood stains on Nick's white turtleneck are lighter, then darker, then lighter again, and migrate to different positions, both during his fight with LaCroix in the abattoir, and throughout the hospital scenes afterward. (00:10:15 - 00:19:30)
Plot hole: Nat thinks Nick is becoming more human because he can see himself in the mirror, and he replies, "Only sometimes." This line contradicts series canon, as "Forever Knight" did not adhere to the vampires-don't-appear-in-mirrors cliché. Nick was seen to reflect very nicely, in fact, every time he passed a mirror, and not just "sometimes."
Plot hole: Near the end, a cop comes to tell Schanke that an explosion has been reported at Nick's place. But neither of the two intruders uses any explosives. One shoots his way in through a door and the other breaks in through a skylight. Neither makes enough noise for the disturbance to be called an explosion. (00:41:15)
Continuity mistake: Schanke calls Nick to tell him they've found Mrs. Hedges' body, and says, "They cut her throat, man." We even see a brief shot of the bloodied corpse. But later in the morgue, Nick says, "She was asphyxiated, right?" and Nat agrees. The corpse on the autopsy table now appears to have an intact throat. So, which way did Mrs. Hedges die? (00:22:15 - 00:38:10)
Revealing mistake: The flashbacks to 1228 in this episode portray some of the same events - Janette seducing Nick, LaCroix making Nick a vampire - that are also shown in "Dark Knight." But here, Nick, Janette and LaCroix are all wearing completely different costumes.
Factual error: The murder victims, all Catholic, are specifically said to have "all worn crucifixes." But the jewelry Nat hands Nick as evidence, the cross that burns his hand and the necklace Magda later gives him are all plain crosses, not crucifixes. (The former is unadorned; the latter has a Christ figure on it.)
Factual error: Nick tells Nat about his past life as an assistant professor in the U.S., and refers to himself as "a certain indigenous vampire." Nick wasn't indigenous (native) to either the US or Canada, where the show was set. He came from Brabant, now part of Belgium. They were probably trying for "itinerant" (wandering), which would accurately describe Nick's long life.
Plot hole: The insertion of a musical sequence used to fill extra time in this episode creates a plot problem. It's spliced in between Nick's urgent plea for Nat to stall the autopsy and his rescuing the bound and gagged Rebecca, and unfortunately makes it appear that in that interval, Nick simply went home, played music and sat in his loft window brooding, ignoring the case altogether. (00:40:40)