<P> Calgary visits retired local doctor, Dr MacMaster, to ask him about Jacko . MacMaster notes that he was surprised when Jacko was convicted for killing Rachel, not because murder was outside Jacko's' moral range', but because he thought Jacko would be too cowardly to kill somebody; that, if he wanted to murder somebody, he would hire an accomplice . While two outsiders attempt to find the murderer, it is insider Philip Durrant whose efforts uncover the truth and force the killer to kill again . Durrant is found murdered . </P> <P> It is revealed that the murderer was indeed acting under the influence of Jacko Argyle . Jacko's carefully planned alibi failed when police could not find Calgary . </P> <P> The killer is revealed to be Kirsten Lindstrom, the Argyles' middle - aged housekeeper . Jacko had persuaded the plain Kirsten that he was in love with her, and persuaded her to murder his adoptive mother under cover of a "foolproof" alibi to steal some much needed money . But once Kirsten learned that Jacko was secretly married, she decided not to cover for Jacko, abandoning him to his fate . </P> <P> Philip John Stead concluded his review in the Times Literary Supplement of 12 December 1958, with, "The solution of Ordeal By Innocence is certainly not below the level of Mrs Christie's customary ingenuity, but the book lacks other qualities which her readers have come to expect . What has become of the blitheness, the invigorating good spirits with which the game of detection is played in so many of her stories? Ordeal By Innocence slips out of that cheerful arena into something much too like an attempt at psychological fiction . It is too much of a conversation piece and too many people are talking--people in whom it is hard to take the necessary amount of interest because there is not enough space to establish them . The kind of workmanship which has been lavished on this tale is not a kind in which the author excels and the reader feels that Miss Marple and Poirot would thoroughly disapprove of the whole business ." </P>

Who is the killer in the book ordeal by innocence