Kenzo Tenma is a very highly-regarded Japanese surgeon living in Germany, with aspirations to someday become the director of the hospital he works at. One night, Tenma ignores hosptial orders in order to save a boy who was shot in the head. Little does he know, this decision would change his life.
This show excels in character writing. Pretty much everyone in the show is great to amazingly written, even ones who only appear for a small number of episodes. Another thing this show does amazingly is build tension. You are constantly on the edge of your seat wondering if a certain character is about to die, or if he'll get away, or if a major character will show up and save him. The music only adds to the stress. The mystery behind the twins' past is also very interesting and haunting.
In terms of psychological thrillers, this is probably the best anime has to offer.