The Submarine Plans: a Hercule Poirot Short Story

The plans for England's new submarine have been stolen from the aspiring Prime Minister. The situation is urgent and Hercule Poirot is summoned late in the evening to crack the case, but none of the witness accounts are the same! Was it an outsider who dashed into the house and snatched the plans, or a member of Lord Alloway's household? Or could it have been a guest? Previously published in the print anthology "Poirot's Early Cases."