Portland detective, Nick Burkhardt, has seen some gruesome crime scenes, but nothing prepares him for the strange visions he begins seeing: seemingly regular people momentarily transforming into hideous monsters. A visit from his only living relative reveals the truth. Nick has inherited the ability to see supernatural creatures, and as a "Grimm," he is tasked with keeping the balance between mankind and the mythological. A reformed "Big Bad Wolf" becomes his greatest (and also reluctant) ally and confidant. It's not long before his work as a policeman leads Nick to the criminals he once thought were only found in fairy tales.
The architect Dana, her husband David and their son Lucas move to an isolated manor in the countryside seeking a restart of their lives after the death of their baby daughter in a tragic accident. Dana overhears noises in the attic and finds a hidden locked room. Soon she finds the keys and is haunted by the evil spirit of an old man. She researches and learns that old rural houses had disappointments room where retarded and deformed children were locked to avoid embarrassment to the traditional families. Further, the spirits of the original owner of the house, Judge Blacker, and his daughter are still trapped in the house. However, only Dana is capable to see and contact them and David believes she is delusional. When Judge Blacker threatens the life of Lucas, Dana tries to protect him but she is not sure of what is reality or daydream.
One day, after returning from work late in the evening, Hideo witnesses a traffic accident in which a car crashes into a nearby pedestrian, killing the victim instantly. However, despite severe injuries including a broken neck, the victim's body stands up and walks away. Hideo questions whether this is another one of his hallucinations, but strange events begin happening around him.