Debbie Mitford

Debbie is a graduate student in sociology when she meets Holden Ford, sharp-tongued and unimpressed by his FBI credentials. She dates him on her own terms, pushes back on his half-formed theories about deviance and criminality, and treats his work as something to interrogate rather than admire. Independence matters more to her than approval.

Hannah Gross gives Debbie a cool, appraising intelligence that keeps Holden honest long before the Bureau does. The show uses her as the audience's skeptic, someone who asks the obvious uncomfortable questions about studying killers that Holden is too enthralled to ask himself. She's never just the girlfriend part.