He's working with a miscast Johnson, a naturally good-natured actor who feels out of place here as Derek, a selfish, cynical minor-league hockey goon. Derek's depressed about the sorry state of his moribund career, and takes out his frustration on young fans, even the daughter of the woman (Ashley Judd) he's trying to woo.
When the little girl loses a tooth and Derek forgets to place a dollar under her pillow, he selfishly tells her there's no tooth fairy, a crime against the children and make-believe so heinous that Derek gets supernatural comeuppance.
He is whisked to Fairy Land and sentenced to serve two weeks as a tooth fairy (shades of the Santa Clause), supervised by Julie Andrews and trained by Stephen Merchant (Ricky Gervais' manager in the British sitcom "Extras").
"Fairy" uses this setup mainly to fuel a series of visual gags - the Rock in a variety of silly or feminine getups, shrunk down to a few inches and chased by a cat, invisible and pretending to be a ghost, or failing miserably at fairy flying school. And, when all else fails, as it does at about the 10-minute mark, he gets hit in the nuts with a tennis ball.
It's best not to think too much about the incoherent plot, which, despite the input of five writers, continues to rely on Derek's lack of belief in fairies, even though he IS one, and spends half his time in fairyland.
It all comes down to the cynical Rock learning to believe - in fairies, in himself, in the power of dreams.
A belief in the power of dialogue and disciplined storytelling would have helped. Even so, the Rock and Judd are appealing enough to make this work for very young, very indiscriminate viewers.