The Dom's Dungeon (Club Chains)

[reprint] Foster child. Teenage whore. Now a veterinarian, MacKensie's turned her life around, but the scars remain. She saves her affection for the animals who never judge or scorn her, but it's time to get out, move on from her past in Iowa. So, she arranges a vacation exchange to job hunt in Seattle. 

Although the house is lovely, one room is locked. Her years in foster care have given her two 'gifts': a neurosis about locked doors and the ability to open them. After she gets into the room, she's appalled...and intrigued. Chains and manacles, whips and paddles, odd benches with straps... 

When Alex returns home days early and finds MacKensie draped over the spanking bench in his locked dungeon, he's furious. But her wariness arouses his protective nature and curiosity, so he strikes a deal to keep her close--she'll act as his submissive in exchange for a place to stay and help finding a job. 

He'd planned to use the veterinarian to deter an ex-girlfriend, not replace her, but with MacKensie's compelling mixture of strength and vulnerability, the little sub slides right into his well-defended heart.