Nick Walker's debut novel Blackbox returns more than once to the idea of "six degrees of separation," and the possibility that all human beings are connected through a surprisingly small number of jumps. But Walker seems to think six degrees is too many; few of his dramatis personae seem to be more than a single step apart. Over the course of 840 extremely short "chapters" (many consist of a single sentence, or even a single ellipsis), which count down from 840 to 1 as the tension grows, Walker leaps from character to character, bending a fistful of parallel plotlines inward until they converge into a series of messy knots. One ostensible protagonist is Blackbox's only first-person character, former airline flight attendant Stephanie Wiltshire. But she appears no more often than anyone else in Walker's tangled web. In one of Blackbox's signature skeins of associations, Stephanie's disturbed pyromaniac brother Edward becomes obsessed with ineffectual therapist-wannabe Ali Bronski after hearing her impersonating a terrorist on Penny Lock's popular talk-radio show. Bronski achieved her greatest success by presenting a paper given to her by Dr. Frankburg, a nervous psychiatrist who was trying to avoid speaking around Clara Redlake, who fell in love with his voice after buying his audiobook. Except that the voice she loves actually belongs to actor Samuel Thorn, who is currently troubled by the apparent suicide of Kirsten Henderson, a young actress who died shortly before her father, Roland Henderson, jumped in front of a train. And Roland's death connects directly back to why Stephanie Wiltshire is no longer a flight attendant. But as Blackbox spells this out, it becomes apparent that Clara is Edward's therapist, and Kirsten was a friend of Ali's, and Frankburg's missing daughter Lily is currently screenwriting Samuel's latest show, and Penny's radio producer is the daughter of the CEO Edward is trying to assassinate… And on, and on, and on, with what comes to feel like dozens of characters and hundreds of connections, by blood, marriage, work, geography, common tragedy, and coincidence. It's a miracle that Walker manages to keep all this coherent, particularly given that his 840 chapters are crammed into just over 300 pages. It's an even greater miracle that he makes such a soap-opera structure compelling. But Blackbox is a bravura debut, a sharp, snappy, skillfully constructed book that reduces a mob of disparate players to pawns in a complex game, yet still grants them their own individual humanity. Blackbox is occasionally farcical, frequently insightful, and often calculatedly clever. Above all, it's an ingeniously gimmicky book that's written with enough sympathy and soul to overcome its own gimmickry.