This isn't an Appleby mystery (although the detective is referenced; I suspect he has recently retired when this story picks up), but I'm glad I read this lighthearted who-done-it. The story is narrated by a first-person tag-team of the young widow, Lady Simney (a former actress who is the first to admit that her in-laws are "dubious") and the assistant police detective, Harold (a Watson type [without a Sherlock] who's writing a letter to his father and has quite a crush on the pretty Lady Simney). 
 The story, which takes place at Hazelwood, the late Baron's estate, is full of Australian relatives, suspected former pirates, anxious pastors, and illegitimate sons, all of whom add a nice mix of crazy flavor. It kept me guessing until the last page and solid in my admiration of Michael Innes.