Nanette Hayes is playing her saxophone on a New York City street, and not taking in a lot of money, when a smart-mouthed young man starts off by insulting her playing, and then moves on to declaring his (platonic) love for her. He says his name is Sig, and it turns out he's looking for a place to crash for the night. Against her better judgment Nan agrees to let him stay the night in her apartment.
She does make him sleep on the couch.
In the very early morning, she wakes up to a very cold apartment.
Her door is open, and Sig is on the living room floor, stabbed to death with an ice pick. And it turns out he's a cop named Charlie Conlin, who has been working undercover investigating a criminal scheme targeting street musicians. That's all bad enough, but after the cops and the body are gone, Nan pulls out her saxophone, and finds that Sig/Charlie had stuffed $60,000 into it before he died.