Codex Books in Order

Codex is Kathryn Nolan's romantic suspense series about a private investigative firm that specializes in recovering stolen rare books. That niche is half the fun. These are not just heists for money. They are cases tangled up with museums, old libraries, wealthy collectors, academic politics, forged identities, and the kind of people who will lie, seduce, or kill to get their hands on something irreplaceable.

The series starts with a simple idea and runs with it: what if a team of smart, capable investigators spent their days chasing missing manuscripts and their nights trying very hard not to fall for each other? Each book follows a different couple, but the world stays connected through the Codex team, their cases, and the larger hunt moving through the trilogy. You get the payoff of a fresh romance every time, plus the comfort of returning to familiar faces.

The first book centers on Delilah Barrett and Henry Finch, and it sets the tone well. Delilah is practical, guarded, and used to danger. Henry is a rare book expert who looks much more prepared for an archive than a criminal underworld. In Under the Rose, the focus shifts to Codex investigator Freya Evandale and FBI agent Sam Byrne, two longtime rivals forced into the same undercover job. In the Clear closes things out with former federal agent Abe Royal and ambitious detective Sloane Argento, whose case puts them in direct competition before it pushes them together.

Yes, the stolen books matter.

Nolan makes the book world feel glamorous and strange without losing sight of the people inside it. The settings help a lot. Philadelphia gives the early books a grounded, old-city feel, full of museums, hidden rooms, society events, and institutions with too many secrets. As the series expands, the story moves through secret societies, European threads, and the shadowy networks that connect collectors, thieves, and investigators. The atmosphere is polished on the surface and dangerous underneath.

The tone lands in a sweet spot between fast-paced suspense and very hot romance. These books have undercover missions, ticking clocks, clues, betrayal, and plenty of tension before the couples ever make it to the bedroom. But they are never trying to be grim crime novels. The mood is bolder, sexier, and more playful than that. Competence is attractive here. So is banter. So is mutual frustration.

If you like your romance with danger, secret passageways, old paper, and people making truly terrible decisions about kissing during an active investigation, Codex is a very good place to be.