Dr. Shin Ha-ru is fired after illegally acquiring a criminal’s brain. He volunteers to help Detective Geum Myeong-se's bureau — and to make him pay.

Ha-ru and Myeong-se's first case involves a famous guitarist and his wife, who turned herself in for his murder. But Ha-ru turns the case on its head.

A Vietnamese woman is found dead with her face and hands burnt. Her husband suffers prosopagnosia; her best friend has disappeared. Both are suspects.

New evidence and test results drastically change the face of the case. A killer approaches Ha-ru, saying he wants to donate his brain to neuroscience.

A 6-year-old with aphasia gets turned in by her mother. She believes a demon has possessed her daughter to kill — and her husband has paid the price.

Ha-ru exposes the truth before the child’s exorcism can take place. And a tablet reveals some dirt on the detective, much to the doctor's delight.

Ha-ru’s attempt to sully Myeong-se embarrassingly backfires. A man reports his wife missing to the police, claiming a "virtual human" attacked her.

After a husband's confession, his wife shows symptoms of conversion disorder. Who killed who? Ha-ru gives up his revenge and leaves the department.

A suspect whose memory resets every 30 minutes claims he has killed his mother. Ha-ru returns, intrigued by a patient with anterograde amnesia.

The stepbrother becomes a prime suspect as the siblings’ harrowing tale comes to light. On his date with So-jeong, Myeong-se gets a call about a body.

The perpetrator who left a mysterious note at the murder scene demands a reduced sentence. Unaware of Dong-u’s plan, Ha-ru appears as a witness.

Ha-ru's statement in court stirs up the media. When he unravels the cause of Kim Mo-ran’s hypersexuality, Myeong-se and So-jeong get tangled up in it.

Ha-ru helps prove I-na's innocence. As he and Myeong-se's family bond, Ha-ru finally discovers Myeong-se’s flaw, leading to his untimely resignation.

Ha-ru learns that his parents weren't killed in a car accident but murdered. To find their killer, Ha-ru must accept a psychopath's dangerous offer.

Myeong-se and Ha-ru must play the sympathy game, or else. The hostages will be released if their brain waves sync. Can two heads work better than one?