Bradley’s constant out-of-the-frying-pan style of storytelling pulls the reader through this tense page-turner. The pace is relentless, leaving little room for character development. Despite the first-person narration, there is a detachment between Callie and the reader that is unusual in YA fiction. Bradley seems reluctant to delve into his protagonist’s inner life. Even the loss of her virginity does not register in any significant way on Callie or the reader.

Callie’s true enemy is unclear throughout, an ambiguity unresolved in this instalment. ‘Something about the creatures had unsettled me on some visceral level, a sense of wrongness,’ Callie recalls of her first direct contact with Changed creatures. But while the reader is told often that the Change is evil, Callie sees the Zone as a safe haven and isn’t repulsed by the Change in her sister. There are hints early on, including in the prologue, that the Change may be benign. The truth will doubtless be revealed in a later book; left unexplained here, it confuses this novel’s tone. Is this a horror in the tradition of The Day of the Triffids (1951), or is it an indictment of humanity’s treatment of the environment like James Cameron’s Avatar (2009)? The lack of any clear resolution in the first book frustrates more than it intrigues.