Crack Down by Val McDermid

When Manchester private investigator Kate Brannigan agrees to let her rock-journalist boyfriend help her with a car sales fraud case, she expects a routine operation. Instead, her world is turned upside down when he is arrested with a trunk full of crack cocaine and illegal contraband. Left to clear his name while reluctantly playing babysitter to his troublesome eight-year-old son, Kate is thrust into a dangerous underworld of drug traffickers and violent enforcers. Relying on her sharp wits and the vital support of her close-knit Manchester friends, including her trusted allies Alexis and Chris, Kate must untangle a deadly frame-up before the gangland violence hits too close to home.