Rachel McAdams and Channing Tatum star in “The Vow,” based on the true story of a wife who wakes up in a hospital after a car accident with no memory of the past five years.

Rachel McAdams wakes up in the hospital after a serious car accident with no memory of the past five years of her life and discovers she’s married to Channing Tatum, lives in a spacious, boho-chic loft and has a successful career as a Chicago artist.

That wouldn’t be so bad, right? Nevertheless, she must reject this foreign existence in her confused state because the plot of “The Vow” requires some conflict.

This old-fashioned amnesia tale would seem totally implausible and manufactured for maximum melodrama; as it turns out, director Michael Sucsy’s film is indeed based on a true story. But it might have been even more compelling with some different casting. McAdams, as the perplexed Paige, is her usual likable self and Tatum, as Leo, once again proves he’s an actor of greater depth than his hunky good looks might suggest.

But what if Paige woke up and found she was married to someone who looked like, say, Paul Giamatti? That might have offered an intriguing little wrinkle. He loves her fiercely and madly and deeply and all those intense proclamations meant to make the teen girls in the audience swoon. He’s willing to fight for her, to help her retrace how they met and what their life together was like in hopes of jogging her memory. He’s even prepared to withstand the condescension and disapproval of her wealthy parents (Sam Neill and Jessica Lange), who wanted her to become a lawyer and from whom she’s been estranged all this time. But he looks like Paul Giamatti.

Instead, “The Vow” serves as a series of precise if obvious moments and emotional cues we must endure en route to the inevitable reconciliation, complete with an intrusively heart-tugging score and too much explanatory voiceover from Tatum.

Give some credit to screenwriters Abby Kohn and Marc Silverstein (“He’s Just Not That Into You”) and Jason Katims: They remain faithful to the real-life story and don’t magically restore Paige’s memories. But the smug parents and the jilted ex-fiance (Scott Speedman) who’s all too happy to rekindle their old romance feel more like pat devices than real obstacles to ultimate happiness.

It’s a nice idea: experiencing what it’s like to fall in love all over again for the first time. McAdams and Tatum sometimes make the execution of it more tolerable than it should be, but not often enough.

FILM FACTSTITLE: “The Vow”CAST: Rachel McAdams, Channing Tatum, Sam Neill, Jessica Lange, Scott SpeedmanDIRECTOR: Michael SucsyRATED: PG-13 for language, partial nudityGRADE: ★★★ (out of 5)