Indulgence in Death is the 31st Eve Dallas book by J. D. Robb. Two bored, wealthy young men begin a "killing game" and it's up to Dallas to make sure each of them loses.
If that sounds vaguely familiar, you might be thinking of the famous real life duo of Nathan Leopold and Richard Loeb. In the early 20th century, two wealthy men from Chicago killed a young boy just to find out what it would be like to murder someone. Indulgence In Death takes the same idea a turns it into a game.
My one gripe with this novel is that Dallas "knows" whodunnit as soon as she meets the young men. There's no question in her mind. She doesn't like them so they did it. There's no detecting needed. The whole book is about proving they did it. It becomes a straightforward police procedural. There's nothing wrong with police procedurals but I expect more from a Dallas novel.
Along with not having a mystery, there's not a lot of the usual interaction between different characters in Eve's life. There's not even that much crazy, hot sex between Eve and Roarke. And that's a damn shame.