Sam and Dean head to Bedford, Iowa, posing of FBI agents to investigate the murder of a woman that had her head smashed by a meat tenderizer by her beloved husband Adam Benson. They discover three similar cases and Dr. Cara Roberts explains that the three husbands had anomaly in their blood work, with the presence of oxytocin a.k.a. love hormone. The Winchester brothers call Bobby and they conclude that a siren might be casting a love spell. Bobby advises that they need blood sample to revert the spell and Sam stays with Dr. Roberts to collect the samples. Meanwhile FBI Agent Nick Monroe arrives in Bedford to investigate the case and he discloses to Dean that in all the crime scenes there was the Mediterranean plant hyacinths. Dean recalls that he had seen the plants in Dr. Roberts' office and calls Sam; however, his brother is having sex with the prime suspect. Dean teams up with Nick to chase Dr. Roberts.