We know almost from the start who the killer is – a handyman of limited intellect known as Walt, but we also know that Walt is getting instructions telling him what to do – in effect, he is a human weapon, while the person using him to kill is hidden. You may recall that Ellery Queen (the author) was a collaboration between Fred Dannay and Manfred Lee, but this book was the first of a sequence produced when Lee had writer’s block. The book was ghost-written by science-fiction author Theodore Sturgeon from a Dannay 42-page outline. It was then extensively revised by Manfred B. Lee, to which Dannay also added some revisions.