What would you do if one of the young lives you saved turned out to be a monster...

Dr. Kenzo Tenma is acknowledged as a brilliant Japanese brain surgeon on the staff of Dusseldorf's Eisler Memorial Hospital and is engaged to the hospital director's daughter Eva. However, two surgeries performed on one fateful day change his life forever. First, a young child (a twin) near death from a severe head injury is rushed to the hospital. Soon after, the city mayor arrives, also gravely ill. When the hospital director orders him to ignore the child and treat the mayor, Tenma refuses, insisting on treating the patient who arrived first. The child survives; the mayor does not, and because he has ignored orders, Tenma finds himself snubbed by the hospital executives, including the hospital director. But then these same top-ranking executives are all found dead under mysterious circumstances. Detective Lunge of the BKA, Germany's Bundeskriminalamt (Federal Criminal Police Office) suspects that Tenma is behindthe crimes, but has no evidence to support his theory.

Nine years after the fateful surgery, Tenma has become head of the hospital's surgery department. One day Tenma sees a new patient --Yunkels, one of several suspects purported to be behind a series of murders of middle - ages, childless couples.

"The monster... is... coming" he warns Tenma, but then disappears a few days later. Searching for him, Tenma finds Yunkles, and there is someone pointing a gun at him. Behind the barrel is none other than Johan, Tenma's patient of nine years ago. Before he shoots and kills Yunkles, Johan tells Tenma that he is behind the deaths of the hospital executives. Then Johan disappears, and now Tenma is the prime suspect behind all of the murders.

Had it been a mistake to save Johan? Tenma decides he must find Johanand learn the truth. But that is only the beginning of his voyage of terror...