Screenwriters, take note: Unless your story is a whodunit, it’s an unforgivable flaw to telegraph early and often that, sometime during the final act, we should anticipate the proverbial rug to be pulled. Every suspicious gesture and line of exposition in The Chameleon teases about what the twist will eventually turn out to be, and French co-writer/director Jean-Paul Salomé’s first English-language feature forgets that the journey needs to compel, regardless. Adapted from a book about a far-out true story that took place during the ’90s, the film stars Marc-André Grondin as a New Orleans teenager (or is he?) who, after vanishing from his Budweiser-swilling, chain-smoking clan three years earlier (or did he?), is discovered near the French Alps with an outrageous story of kidnapping rings, rape, memory loss, and accent gain from being forced to speak French. Back at “home,” he now broods, his sister (Emilie de Ravin) openly welcoming him while his volatile half-brother (Nick Stahl) and dead-eyed mom (Ellen Barkin) warily tolerate his presence. Improbable FBI agent Famke Janssen tenaciously asks her boss for one more week, maybe two, to get to the bottom of this fishy reunion. Is he an imposter? And if so, why has the family embraced him? And why aren’t the psychological, emotional or moral implications of the maybe-lies ever explored in this dreary drama?