When There Is PeaceLost Like Me Crossover between Agatha Christie's Poirot Books and Jeeves and Wooster, where Hastings and Jeeves had a relationship during the war and reconnected years later. In the sequel, Bertie and Jeeves happen to be at a party where Poirot and Hastings are investigating a possible murder-to-be.
I very nearly recced these stories because they're well-written and feature small fandoms and because I do like the Jeeves and Wooster bits. Unfortunately, these are very much Poirot stories first and J&W stories second and a) it's been ages since I read a Poirot novel and b) I have a really, really tough time pairing Poirot with anyone. Since at least half of the second story is about the Poirot/Hastings relationship and most of the rest is devoted to an ultimately unsatisfying mystery (we don't get many clues and the resolution mostly involves stuff that apparently happened off-screen), the lovely Bertie/Jeeves slivers just aren't enough for me to rec.
That said, if you are a Hastings/Poirot shipper, you should absolutely give these fics a try, because they're the longest Poirot fics I've ever read and for the most part the writing is top-notch.