Poirot is more in the mix in this novel than either a central character or  a welcome rescuer. He pops up, then disappears, then pops up, then disappears. This would be fine if the main characters were truly appealing (or appalling) but with a single exception they do seem to just be a pile of wet laundry.  The big revelations at the end are weirdly unnecessary (if you think about what the culprit says earlier in the book it makes sense that they could just be a little more of who they seem to be and the answer would be the same), meaning that the puzzle elements are also unsatisfying. Unless you're a real Poirot-head (that's what we call them, right?!) you can skip this one.