2.5 stars. 
 Overlong and a little boring. The cliffhangers that don't amount to much feel gimmicky and frustrating. The pace feels odd, and the premise is a bit sad. Not a favorite, but still, Moriarty writes a compelling novel. The fact that I didn't love this but HAD to finish all 400+ pages just to know what happened is a testament to her skill. 
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 Full review: 
 Moriarty has a knack for writing about people: the complexity of their relationships and the subtle shifts in their emotions. She also has a knack for setting up cliffhangers to keep you reading, even when the previous dozen cliffhangers were frustratingly anticlimactic. But that combination of (ultimately unsatisfying) plot tease and (somewhat satisfying) emotional relatability is what keeps me reading 400+ pages of a fairly dull story. 
 This book starts out intriguing enough... something happened at a backyard barbecue, something dramatic enough to upend the lives of three different couples and their families. And if we're to believe the title, someone is "Truly, Madly, Guilty." 
 Or not. The pace is achingly slow. The plot, as it unfolds, is increasingly dull and sad, not sinister. When that initial coyness suggesting a mystery finally delivers a mundane revelation of what actually happened, I find myself thinking, "That's all?!" 
 Still, Moriarty can write. She can write people, personalities, and the sticky tensions of domestic life. Pick this book up for those reasons. If you're looking for a twisty mystery involving murder or madness or actual guilt, move along.