Love is a losing game, love is a numbers game, and sometimes it’s both. Ally Darling lives in a world easily mistaken for that of Carrie Bradshaw, in which magazine fluff pieces could still send a girl’s head into a spin. One article in particular reads like the death rattle of Ally’s last viable egg. It postulates that number of sexual partners has an inverse correlation with happiness; sleep with enough guys, the theory goes, and you ain’t never gone git married. The headline also happens to be “What’s your number?” so, you see, it’s not just a clever title.

Anna Farris is an actress who throws herself into work like no other I can name. She has been in so many bad movies – almost irredeemable movies – and yet somehow managed to convince us of her unshakeable belief in each and every one. That’s an admirable quality which serves her just as well when the material has a modicum of potential. What’s Your Number remains stubbornly derivative and oftentimes forgettable. It is not Lost in Translation, or even Just Friends. But as a genre exercise and easy Friday night rental, it succeeds more often than not.

The article puts the average number of sexual partners at 10.5, which kinda has to make you wonder about the half. Ally’s total is a slightly less chaste 19, and not an especially good 19 either. One was Gerry, the puppeteer, who kept the puppet on throughout. Then came Gay Tom, and Eddie who wanted to keep it casual. Disgusting Donald was just that, while Jack emigrated to Africa to head up the kind of worthy foundation you see on TV charity appeals. The list goes on, and Ally revisits them all in the hope one might have blossomed into the proverbial frog prince. A sweet fairytale, perhaps, except one of those Prince Charmings is now a gynaecologist, who recognises her only upon renewing acquaintance with her vagina.

That’s a word you’ll hear more than during the course of the film, owing to a script clearly liberated by last year’s R-Rated Bridesmaids. Of the two, this is the more traditional fare, which is to say it never stoops so low as to recreate that bridal shop scene. Not that it has an overly positive message of its own, but it can at least find comfort in not having utterly demeaned its intended audience along the way. Such an opinion is unlikely to find many supporters. If this had only come with Judd Apatow and an SNL alum attached, the reception might have been considerably warmer.

Even so, there’s no more than half a movie here. The first hour does its best to bury anything not frighteningly predictable. Ally rekindles relationships best left forgotten, and dissuades the rest with clumsily laid plans. On she goes, the little blonde hamster in her wheel of futility, until she finally comes to rest upon a handsome neighbour. For a while he was just some jerk from across the hall, with a stream of conquests emerging to a walk of shame every morning. But wouldn’t you know? With just a little movie magic and curtains drawn back, his true self is revealed: a thoroughly charming Chris Evans, muscular, topless and yours.

That’s the game right there. It’s why this movie works. A co-star Farris’ equal, whose energy combine with hers to transform the film. Skinny dipping, late-night basketball, and a habit of making the big gestures: in rom-com terms he’s a home run, and what more could a girl ask for? Farris has never seemed happier. It’s like all those years of hoping, praying and believing have finally given her an okay-to-average movie worth fighting for.