Holmes is visited by Mrs Merrilow, a landlady from South Brixton who has an unusual lodger who never shows her face. She saw it once accidentally and it was hideously mutilated. This woman, formerly very quiet, has recently taken to cursing in the night, shouting "Murder, murder!" and "You cruel beast! You monster!" Also, her health has taken a turn for the worse, and she is wasting away. Mrs Merrilow has brought this case to Holmes's attention as her tenant, Mrs Ronder, will not involve the clergy or the police in something that she would like to say. She has told her landlady to mention Abbas Parva, knowing that Holmes would understand the reference.

Indeed he does. It was a most tragic case in which a circus lion somehow got loose and savaged two people, one of whom was killed, and the other badly disfigured. The latter is apparently this lodger – the former was her husband. Holmes could make little of the case at the time, but perhaps if someone had actually hired him, the outcome would have been different. As it was, the inquest ruled that Mr Ronder was the victim of death by misadventure. Still, even the local police were a bit disturbed at the time by some seeming inconsistencies in the accounts. For example, the lion was part of an act which Mr and Mrs Ronder performed right in its cage, and they were the ones who fed it. Why had it suddenly turned on its feeders? Why had it not tried to escape? Who was this man that several people heard screaming when supposedly Mr Ronder had already been killed?