Patel’s power saves disjointed view of a search for home

Knowing the ending in advance is usually considered detrimental to effective filmmaking, but a smart director and screenwriter can use foreknowledge to their advantage, if they work it right. For much of the way, director Garth Davis and screenwriter Luke Davies work it right in “Lion,” the fact-based story of a young man who goes in search of his lost childhood.

The first half of the film is short on dialogue but eloquent in storytelling as a young Indian boy named Saroo (Sunny Pawar) gets separated from his older brother Guddu (Abhishek Bharate) one night, winds up on a decommissioned train and ends up a thousand miles from home in Kolkata (formerly Calcutta).

Unable to communicate with others because most people in the teeming city speak Bengali and he only speaks Hindi, Saroo wanders the streets and somehow survives on his own until he’s rescued, sent to an orphanage, and adopted by an Australian couple named John and Sue Brierley (David Wenham and Nicole Kidman).

For much of the way at this point, we have viewed a vast and confusing world through the eyes of a lost child. Suddenly, he’s on an airplane heading for Australia, looking down on the world in a scene that foreshadows the film’s second half and the mechanism the adult Saroo will use to search for his past: Google Earth.

Davis relies heavily on Greig Fraser’s cinematography to tell the story at this point — a whirl of golden butterflies circles Saroo in the opening scene, then the world becomes dark, soot-filled and misty as he looks desperately and in vain from the windows of the speeding train for some familiar landmark. Young Pawar handles his scant dialogue well enough, but we focus on his face and especially his enormous, expressive eyes to tell us about Saroo’s confused feelings of anxiety and curiosity in a strange new world.

Dev Patel plays the adult Saroo in the film’s second half. Now Saroo is studying hotel management, beginning a relationship with a fellow student named Lucy (Rooney Mara) and considering the Brierleys the only mum and dad he’s ever known.

When asked about his childhood in India, his answers are vague and evasive — he says only that he’s from Kolkata and doesn’t remember much about that time.

And then, at a party, something seemingly irrelevant happens that flips the switch of memory in his mind, and he becomes obsessed with reconnecting with his mother and his past.

Patel’s performance carries the weight of the second half of the film so well, you may overlook how badly the two parts of the film are married. Now everyone talks — a lot — and as they do, the eloquence of the story is imperiled. Where Davis and Davies were able to achieve sweep and dimension in Saroo’s initial separation from his mother and brother, now they rely on series of quick, underdeveloped scenes that may momentarily capture our curiosity but are so fleeting we can’t really invest in anything except Saroo’s determination to find out how he became lost all those years before.

Patel delivers a definitive, star-making performance, one that fills in all the considerable gaps in the script and reaffirms his versatility as an actor. Ill-served as he is by the dialogue, he still makes Saroo credible and heartbreaking, even as the character touches the edge of madness in his desperation to get home again. Patel has done very good work in films like “Slumdog Millionaire” and “The Man Who Knew Infinity,” but “Lion” catapults him to the top of his profession.

Kidman also overcomes script weaknesses that fail to establish Sue’s fragile character until a revelatory scene in which she releases all of her fears. The scene is powerful and only makes us wish she’d been given more room to stretch elsewhere in the movie.

Where the first half of the film had power and sweep, the second half is a bunch of Post-it notes. In spite of that, and because of Patel’s electrifying and deeply nuanced performance, “Lion” ultimately delivers the emotional punch it has promised all along.

Lion

Drama. Starring Dev Patel and Nicole Kidman. Directed by Garth Davis. (PG-13. 118 minutes.)