This has a two for oner:  First there is the introduction of Inspector Henry Christmas of Scotland Yard, and then there is the saga of Plum....she's about to have everything an orphan could want--her best friend explains to Mrs. Bradley and George (her trusted driver), "My parents are adopting Plum by Christmas."  Of course, this being a mad cap Mrs. Bradley mystery, things don't always go according to plan!  Oh, and there is also a Mr. Valentine...

"Mr. Valentine"