Barnard meets some of the usual objections to Christie (her characters are wooden stereotypes, her writing is bland and uninteresting) and shows that while there's a bit of truth in them, the characters and writing serve her purposes well. Writing that does that shouldn't be undervalued even if the prose doesn't rise to the level of Joyce's.
I read quite a few of Christie's books at one time, and I still read one now and then, if only to marvel at her ability to fool me completely. Her plotting is second to none. There's also a bit more humor and wit in her books than most people seem to realize. If you're like me, then you're the audience for this book. Barnard assumes a certain amount of familiarity with the novels, and he works hard not to give away the solutions to Christie's puzzles, especially in his capsule summaries. If, on the other hand, you've never read much of Christie, I suspect you'd want to after seeing what Barnard has to say in this book. Check it out.