Among the great mysteries of contemporary cinema: how, in the space of one year, can a director make something as good as Belfast, and follow up with the ridiculous Death on the Nile? I don’t think one can lay the blame on an overbearing studio, or suggest that the best of Kenneth Branagh’s movies may be the ones in which he doesn’t appear. This may be true of Woody Allen, but Branagh is known primarily as an actor. That leaves only two possibilities: money or mental derangement.