The tale of a 32 year-old failure (Adam Brody) who was once his town's most celebrated child, it spends much of its time looking, with some humour but little mockery, at how it feels to fail to live up to one's potential. But it's also the mystery yarn its title suggests, and one whose darker moments require us to point out that, title notwithstanding, this isn't quite a family film.

In voiceover, Brody's Abe Applebaum seems to be setting us up for cute comedy as he recounts his Encyclopedia Brown boyhood: His office was a treehouse, where he charged four bits to solve mostly harmless mysteries in a world not far removed from 1950s white-bread America. Boasting the kind of weird insights into human behaviour that probably only hold true in fiction, he righted enough wrongs that the mayor eventually gave him the key to the city. But then came a case that was close to home and unsolvable.

Now a boozy pariah, he continues to straggle into an office with the private eye's requisite pebbled window and indifferent secretary but rarely gets work beyond finding lost cats. His parents bring groceries and judgmental concern whenever they visit his home.

Then a real case arrives. High-schooler Caroline (Sophie Nelisse) wants Abe to find the person who killed her boyfriend Patrick, by stabbing him 17 times.

Everyone in town knows Abe shouldn't get involved, given his lack of success solving serious crimes and his overall failure to maintain grown-up standards. But his heart goes out to Caroline, an unworldly orphan. He warns her she may learn things she'd rather not know about the boy she thinks was as uncomplicated and good as she is.

The fact that Abe is quickly proven right keeps us believing in the keen-observer persona he still clings to. But slowly, especially when Caroline starts joining him in his pursuit of leads, we realise how often he is blind.

Evan Morgan's script generously allows us to deduce the truth just before Abe stumbles across it, which is not to say it doesn't have some real surprises left. It's fun to watch Abe put A and B together, and to regain some of his self-respect in the process. But even victory will bring mixed emotions, which Morgan conveys with unsettling finesse.