Second paragraph of third chapter:

“Can I help?” said Antony politely.

This is by far the best known book by Milne outside the Winnie-the-Pooh mythos. It’s a locked room murder mystery published in 1922, where the long lost brother of the owner of the Red House turns up mysteriously dead in the library, and the owner himself disappears. For the attentive reader, it’s fairly obvious who the murderer is from the moment it happens, but the full details of the mystery are delightfully worked out by Antony Gillingham, who just happened to be visiting his friend Bill at the Red House and arrived exactly at the moment of the murder. There’s a hilarious and improbable secret passage ending in a croquet box (illustrated on the original front cover, so I don’t think this is a spoiler).

Antony and Bill role-play Holmes and Watson through the (short) book, but I think Milne is hinting that they are more than just friends, in the closeted upper-class way of the time.

Also interesting that there is no reference at all to the war. (We are told in a throwaway remark that Bill learned Morse Code in the Army.)

You can get The Red House Mystery for free on Project Gutenberg, or pay for it here.