Nick, Juliette, Hank, and Trubel return to the house after dirty FBI agent/Hundjager Weston Steward shot Captain Renard before being decapitated by Trubel at the end of the Grimm Season 3 finale.
Despite the apparent strangeness of a young woman decapitating a man with a machete, neither the Portland Police detectives nor the FBI agents find anything to contradict Trubel's story of self-defense, but one of the agents is a Steinadler who shows a surreptitious interest in the young Grimm.
Sgt. Wu grows ever more suspicious, having seen one of Nick's Grimm diaries in Trubel's room. He confides in Hank, knowing that Hank had suffered his own issues after having seen something he couldn't explain. Hank attempts to give him some moral support in his internal struggle.
Nick tries to come to terms with the loss of his Grimm powers thanks to Adalind's deal with Renard's cousin Prince Viktor. Monroe and Rosalee immediately offer to help figure out what it was that Adalind did to him and try to fix it, although Nick starts to wonder if losing his Grimm powers might give him the chance at a normal life with Juliette.
Prince Viktor learns of Weston Steward's attack on Renard and is determined that his uncle the King not discover that Steward worked for Viktor, since the King has a great deal of affection for his bastard son. He gives orders that evidence be planted linking Steward to Nick instead of him.
Meanwhile a mysterious octopus-headed Wesen also attacks a defense contractor scientist, stealing his memories and leaving him alive but suffering from dementia. The Wesen kills the man's unsuspecting girlfriend when she returns home unexpectedly. He then uses the scientist's memories to infiltrate the data network of his company and download sensitive data.
The Wesen is taken into custody after he is caught with the victim's car. Nick and Hank suspect he's Wesen, but with Nick down for the count in the Grimm department, they can't prove it. They release him and set Trubel to follow him.
Even as Nick and Hank investigate with Trubel's help, Captain Renard takes a turn for the worse in the hospital. A mysterious blonde woman looks on as he flatlines and the doctors call his time of death.