`The Perfect Murders' is a collection of four Agatha Christie novels and like all Christie's books they are masters of detective fiction. However there are other Poirot novels that might make a claim to be included in any volume headed `The Perfect Murders'. Of course `The Murder of Roger Ackroyd' is well narrated and possibly the best murder mystery ever written. `Murder on the Orient Express' is ingenious with a host of international characters. Both could be described as perfect murder mysteries.
However the latter two books do quite belong in a collection entitled `The Perfect Murders':
`Murder in the Mews' keeps you guessing but violates the 18th rule of Detective Fiction and would've been better suited to a short story collection. `Hercule Poirot's Christmas' is well contrived, like all of Agatha Christie's books, but it was more classic than perfect.
All in all a good way to group together Poirot novels that couldn't easily be categorized, though Harper Collins might've been more thoughtful about which books were `perfect' and which were `classic' after all `perfect' is a very subject word.