Plot hole: Bullets, which have been passing harmlessly through Nick for two whole seasons, suddenly do him great injury here. And though he's taken to surgery, the bullet lodged in his head is never removed. It's still there on the latest x-ray when LaCroix arrives to "consult" with the doctor.
Plot hole: In a major violation of series canon, this episode ends with the vampire doggie (a silly enough premise to begin with) bringing its owner across, a process previously established as complex enough to be far beyond even the smartest canine's capabilities.
Plot hole: Because he has no discernible vital signs, the wounded Nick is declared dead in the hospital. When he revives, he's rushed into surgery, where he'd surely have been reattached to a monitor. Somehow, though, no one on the medical staff notices that their patient still has no normal pulse or heartbeat.