Some books start at point A, take you by the hand, and carefully walk you to point B, and on and on.   This is not one of those books. This book is about mood, and how it works in and with us as complicated, imperfectly self-knowing beings existing in a world that impinges and infringes on us, but also regularly suffuses us with beauty and joy and wonder. You don't write that book as a linear progression--you write it as a living, breathing, richly associative, and, crucially, active, investigation. Or at least you do if you're as smart and inventive as Mary Cappello.   What is a mood? How do we think about and understand and describe moods and their endless shadings? What do they do to and for us, and how can we actively generate or alter them? These are all questions Cappello takes up as she explores mood in all its manifestations: we travel with her from mood rooms to art installations to off the beaten path natural history museums, to the more scientific corners of topics like depression and synesthesia, to jazz improv and, of course, the countless writers who have attempted to pin down just what this central aspect of being human is and means. The result is a book as brilliantly unclassifiable as mood itself, blue and green and bright and beautiful, smart and sympathetic, as powerfully investigative as it is richly contemplative.   "I'm one of those people who mistrusts a really good mood," Cappello writes early on. If that made you nod in recognition, well, maybe you're one of Mary Cappello's people; you owe it to yourself to crack Life Breaks In and see for sure.