Zero Hour by Megan Erickson

Hacker extraordinaire Roarke Brennan lives each hour – each breath – to avenge his brother’s murder. His first move: put together a team of the best coders he knows. They’re all brilliant, specialized, and every one an epic pain in his ass. Only now Wren Lee wants in too, threatening to upset their delicate balance. The girl Roarke never allowed himself to want is all grown up with sexy confidence and a dark past … and she’s the wild card he can’t control.

Roarke might still think she’s a kid, but Wren’s been to hell and back. Nothing and nobody can stop her – especially the tatted-up, cocky-as-all-hell hacker. But when years of longing and chemistry collide, Wren and Roarke discover that revenge may be a dish best served blazing hot.