The Sin Losers by Alan Marshall; Donald E Westlake

Perverse Prisoner. Having been a prisoner of her own lusts, the insatiably wanton demands of her body, Maryann was determined to escape her life of degradation. Her lover, Hubert, finally left the depraved clutches of Ethel, his wife, but she continued her evil clutch. As Hubert and Maryann had a brief glimpse of ecstasy in the secluded motel, writhing through their sensual passions while the authorities battered down the door to their . Carnal Cage!