Here's a curiosity from Westlake's canon, one of the few non-fiction books he wrote during the course of his prodigious career (the only other one I know of is the biography of Elizabeth Taylor he penned under the nom de plume John B. Allan):
This is the UK paperback edition of Under an English Heaven, published by Hodder & Stoughton in 1993. And it's curious for a couple of reasons, quite apart from it simply being non-fiction. Firstly, there's the subject matter, which isn't exactly something you'd expect a crime/caper author like Westlake to pick: it's about the 1969 invasion of the Caribbean island of Anguilla by over 300 British paratroopers and marines, and the reasons for and events leading up to it. It's an obscure period of colonial history that I doubt many Brits would even be aware of (I certainly wasn't) let alone anyone else, but evidently it chimed enough with Westlake – who presumably would've known about it at the time – for him to explore the invasion and try and find some comic potential in it.
Secondly, there's the matter of this particular edition of the book. Under an English Heaven was first published in 1972 in hardback by Simon & Schuster in the US. Hodder picked up the rights for a UK hardback edition in 1973... and that was that. There were no other editions for twenty years, until this UK paperback was published. Except, it doesn't seem to have been properly published. My copy has no barcode or ISBN number on the back, and no price either. The interiors, meanwhile, are a straight rerun of the '73 interiors, with no post-'73 books listed under "Also by Donald E. Westlake", and only an extra line added to the indicia stating "This edition 1993". On top of that, the paperback is incredibly scarce: there are a couple of dozen or so of the S&S and H&S hardbacks listed online, but only a handful of these Hodder paperbacks.
There are a few possible explanations. One is that the paperback was only printed as a proof or review copy ahead of a new edition, perhaps a new UK hardback – there is a 1993 hardback listed (but unavailable) on Amazon US, although not on Amazon UK – that never materialised. Another is that it was produced for an event of some kind; some of the few paperbacks floating around the web have been signed by Anguillan politician Jeremiah Gumbs. Or it could've been printed for contractual reasons: publishers have been known to produce copies of books just to keep them officially 'in print', thereby keeping hold of the rights. I have no idea what kind of contract Westlake signed with Hodder, but the fact that this paperback appeared exactly twenty years after the UK hardback might be significant.
It's an intriguing little mystery. Perhaps one day I'll get to the bottom of it...