A young woman is violently killed, and Team Grimm is called in to investigate. Due to the nature of the crime, Nick immediately suspects Wesen involvement, but he's not able to find any apparent motive.
At the same time, an elderly woman suffering from dementia attacks an orderly at her care facility, and he is forced to defend himself after she woges on him.
No one believes him when he claims that the elderly woman turned into a monster, but that night an insectoid Wesen sneaks into her room. She turns up dead the next morning.
The medical examiner finds a large amount of insect saliva in her system, from a creature known as an assassin bug. Nick and Hank immediately suspect Wesen involvement and turn to Monroe and Rosalee.
Monroe and Rosalee explain that the creature they are seeking is called a grandfather of death, and they occupy a unique place in the Wesen community.
When a Wesen suffers from dementia, the grandfather of death is summoned by caregivers to give them a quick and easy death before they possibly harm someone else or expose the Wesen community.
The elderly woman and the original murderer were both suffering from dementia. Team Grimm leaves the grandfather of death to do his duty.
Meanwhile, Eve continues to investigate the mirror problem and eventually discovers a spell to let her cross into the other realm. Despite their earlier protests, she casts the spell and passes through on her own.