In the stage play Black Coffee, Dr Carelli is an Italian physician who turns up at Abbot's Cleve, the home of Sir Claude Amory claiming to be a friend of Lucia Amory and becomes a house guest.
As Carelli comes from Lucia's native Italy, at first, Lucia's husband Richard Amory suspects that the pair are romantically involved. However, as Poirot discovers, he is there for a darker reason because he knows something about Lucia's mysterious past.