"Informed Risk" by Robyn Carr (bonus book "A Hero for Sophie Jones" by Christine Rimmer)

Mike Cavanaugh was a firefighter; it was his job to rescue people. Though inviting them home wasn't usually part of the job description. But when he pulled Christine Palmer out of her burning house, something about the gutsy single mom made him want to protect her, to make her life a little better. Only somehow Chris and her family ended up giving Mike's life new meaning, and he was happier than he'd been in years.

But Chris was smart and resourceful. She'd get back on her own two feet -- sooner rather than later. And when she no longer needed Mike's support, would she still want his love?

"A Hero for Sophie Jones" 

Heartless seduction was Sinclair "Sin" Riker's stock-in-trade. So what was it about the innocent Sophie Jones that made Sinclair want to turn from 'sin' to saint?