When a woman is raped in Central Park, Stella's mission to find the attacker is hindered, as the victim has no memory of the assault. Despite the abundant evidence at the crime scene, the detectives can't connect a suspect to the rape, frustrating Stella, who commits herself to nailing the attacker. Meanwhile, Mac and Aiden must track down an evidence-swallowing rat when they investigate the shooting of a drug dealer. After inspecting the body, Dr. Hawkes discovers that not only is the bullet missing, but that the victim has rat footprints and bites on his body. Now, the team needs to find one rat in a city with 70 million of them in order to gather the evidence that will lead them to the murderer.