Bungou Stray Dogs: Out of One Prison and into Another

Atsushi woke up in dark prison cell. He didn't remember what happened or how he got there. A man comes to him one day, offering him a way out. What else can he do? He takes the opportunity to get out of the prison, but that may have been a mistake.
AU where Atsushi joins the Port Mafia as Dazai's apprentice.