Officer Nadia Santiago

Santiago is not a villain; McManus depicts her as a competent professional following the evidence available. She serves better as a structural antagonist: the pressure she applies to the four suspects arises from institutional process rather than personal malice or corruption. Her arc ultimately ends with her facilitating Jake Riordan's arrest, showing that she pursues justice even when she initially targets the wrong person.

Santiago arrests Nate Macaulay when fabricated evidence surfaces that points directly at him. His prior drug conviction had already positioned him as her primary suspect, providing a clear criminal profile to target. The arrest represents the novel's dramatic low point, illustrating how easily an institutional investigation can be manipulated by someone — in this case, Jake Riordan — who understands exactly how the system functions.

Their relationship is the most adversarial in Santiago's arc. She pursues Nate more intensely than any other suspect because his drug record makes him the most legally vulnerable of the four detainees. McManus uses this pairing to examine how a prior criminal record can shape presumed guilt — not through corruption, but through the institutional logic of treating a known offender as the likeliest suspect.

Santiago interrogates Bronwyn repeatedly, focusing on the academic-cheating motive that Simon had planned to expose. Bronwyn's careful, lawyerly responses consistently frustrate Santiago's attempts to find a flaw in her story. Their dynamic creates a distinctive intellectual friction — both characters are analytical and strategic — and McManus uses it to highlight the limitations of interrogation against a suspect who fully understands the rules of the encounter.

Santiago's investigation follows the path of least resistance: the four students present in the detention room. Jake is popular and seemingly peripheral, placing him outside the investigative pathway created by her evidence. McManus highlights this blind spot to make a thematic point about institutional justice — official investigations can be dangerously susceptible to tunnel vision, and Santiago only considers Jake once the teenagers' grassroots investigation reveals new facts.

Santiago does not solve the case independently; it is the four suspects' investigation that exposes Jake Riordan as the true perpetrator. Santiago's role at the novel's resolution is to facilitate Jake's arrest once the truth is revealed, rather than to discover it herself. McManus presents this as a muted vindication: the system ultimately delivers justice, but only because the teenagers outpaced it.

Santiago questions both as detainees present at Simon's death, but neither interrogation opens the case. Addy's apparent passivity initially deflects suspicion away from her circle, even though her relationship with Jake is ultimately the novel's most critical link. Cooper's evasiveness — stemming from guarding his sexuality, not guilt — complicates his cooperation with authorities without giving Santiago any real leverage against him.

Santiago embodies the gap between institutional authority and actual truth. McManus uses her to critique systems rather than individuals: Santiago is neither corrupt nor incompetent, yet her process endangers an innocent person and overlooks the real killer for much of the novel. Her arc illustrates how institutional investigations follow pre-existing pathways — prior records, circumstantial evidence, established social hierarchies — instead of the messy, relational truth the teenagers uncover.