When Uncle Ben's Dublin business fails, it's clear to Gloria and Raymond that something is wrong. He just isn't his usual cheerful self. So when the children overhear their granny saying that the Black Dog has settled on Ben's back and he won't be OK until it's gone, they decide they're going to get rid of it.

Gathering all their courage the children set out on a midnight quest to hunt down the Black Dog and chase it away. But they aren't the only kids on the mission. Loads of other children are searching for it too, because the Black Dog is hounding lots of Dublin's adults. Together - and with the help of magical animals, birds and rodents - the children manage to corner the Black Dog . . . but will they have the courage and cleverness to destroy the frightening creature?