This is a question I get fairly often. Here is a synopsis.
The Former Hero, by Jeffrey Mays
An abusive, alcoholic, single mother goes into a frenzy when she learned her daughter, Penny, is abducted. City services have fallen into decay because of rampant corruption, and she is unable to reach the police. She sets out on her own to find the girl and solicits the aid of Angus, a surly profligate on a motorcycle. They learn of 
Lieutenant McCarthy, a detective and the only remaining good cop in the city. McCarthy has been sidelined for his refusal to join the new police union, and spends his days reading the ancient city records researching the early stories and characters of the city’s history.
Meanwhile, a man referring to himself as ‘John Common’ checks himself into a hospital seeking help to recover his superpowers. He tells doctors that until recently he was Omni-man, superhero of tremendous powers, and the only hope for overthrowing the villainous tyrants who have taken over the city, and their leader Mayor Robert Knox. Doctors keep Omni-man for several weeks under surveillance, assuming he is under a delusion rather than a deflowered superhero. Frustrated with their evasions, he overpowers a nurse and breaks out of the hospital.
Detective McCarthy, stewing over hard memories of his deceased father and wishing for new crime-fighting assignments, returns to the record storage room and discovers that a primeval villain, Lucy Burden a.k.a. The Minstrel, caused much heartache and mayhem in the years when the city was young. She was, he learns, the first villain and grandmother of the current crowd 
of real villains, and the lingering spirit that breeds corruption in the city. He bitterly questions why the comic book heroes are not real, but the villains are.
Through a series of adventures, McCarthy, Mary the mother of Penny, Angus the biker, and the Former Hero find themselves on a bus together with a clue to where Penny might be held. The surprise ending tells what happened to Penny, what the Former Hero’s true identity is, and how Mary comes to grips with her addictions and abusiveness toward Penny and her estranged husband.
