The Jump by Martina Cole

Donna Brunos worships her husband and is devastated when he is jailed for armed robbery. Georgio swears he's been set up and persuades Donna to help him escape. Implementing 'the jump' takes Donna into a twilight world she never believed existed - a world of brutal sex and casual violence. Finally, she is confronted by a series of shattering revelations that threaten not only everything she believes in but also, ultimately, her own life...