Hercule Poirot's Last and Greatest Case.

Colonel Hastings and Hercule Poirot return to the house where their partnership began. Hastings is now a widower, with a grown-up daughter (also staying at the house); Poirot has become a very old man. Poirot recruits Hastings to help him hunt down a killer who has been undetected for decades, leaving ruin behind. Murders, attempted murders, suicides follow soon upon their arrival at Styles... but were they really suicides, attempted murders, and murders? Were the obvious perpetrators actually innocent, yet more victims for the mysterious X?