In 1986 and 1987, two of Anthony Horowitz's earliest novels, the first two Diamond Brothers books, were published by Grafton Books (with paperback editions later printed under their Dragon imprint) -- The Falcon's Malteser (pictured above with its original cover), and its sequel Public Enemy Number Two.
In 1988, The Falcon's Malteser was adapted as a film, retitled in the UK as Just Ask for Diamond, and Lion Books published a new edition of the book tying in to the movie. The following picture of that edition was provided by Giles Leigh:
In 1991, a third book featuring the Diamond Brothers, South by South East, was published, at the same time as a TV serial that was either an adaptation of the book, or the book was a novelisation of the TV series (I haven't entirely worked out the relationship between the two yet, but you can read all about my attempts to do so here) began its one and only UK transmission. In any case, Lion Books also published the original version of that third book, and it looks like this (I have thanked Christian Bernard-Gauci for first putting me onto the existence of this original version before, but let's do so again, especially since it's his picture).
At the same time, Lion also reprinted the first two books in the series. Thanks to Jonathan Craig and his brother, who dug out their old copy for me, I am able to provide what I believe to be the first ever picture on the Internet of what the 1991 reprint of The Falcon's Malteser looked like:
Then, in 1995, the books were taken up by a new publisher, Walker Books, who continue to print the series to this day. But when the books were reprinted by Walker, all had some significant alterations made to them. If you have any of the older copies pictured above, then you have the original version of the text (thanks to Giles and Jonathan, I have confirmed that there are absolutely no differences whatsoever between the '86, '88 and '91 versions -- all three are even typeset the same). If you have any Walker edition, then you have the revised version.
(Note that I do not know anything about non-UK editions of the books, but if you have any information you'd be willing to volunteer about them it would be welcome. There is one other pre-1995 version of the book published in the UK not mentioned above: this, which appears to be an omnibus of four children's adventure books from different authors that were all published by Lion. I see no reason to think that the version of The Falcon's Malteser contained therein is any different, but if you have a copy then I would be grateful for absolute confirmation.)
I have already given an overview of the differences between the original and updated versions of South by South East here, as part of my quest to learn as much as possible about the TV series. But doing that post prompted me to track down the original versions of the first two books -- I'd always been curious about the two copyright dates in the Walker editions indicating there was a different version originally published -- and here we have the differences between the 1986 and 1995 versions of The Falcon's Malteser, with Public Enemy Number Two to follow at some point in the not-too-distant future. As with the earlier SbSE comparison, this is not an exhaustive list of changes, just the salient ones -- pretty much everything not covered here is minor changes to punctuation and removing hyphens from the middle of words.
