The story begs for the big screen: In 1986, five-year-old Saroo Brierley, the youngest member of a family in the impoverished Indian neighborhood of Khandwa, got stuck on a train. He traveled close to 1,000 miles across his country, wound up in a shelter and eventually was adopted by an Australian couple. Some 25 years later, equipped with Google Earth and vague childhood memories, Brierley retraced his path and found his way back to his birth mother. Cue the tears.

“Lion,” the first feature directed by Garth Davis, sufficiently realizes the emotional arc built into Brieley’s experience. Adapted from his book “A Long Way Home,” the movie features a sturdy Dev Patel as the intense young Saroo eager to reconnect with his roots, but the movie’s best moments precede his arrival. In its first hour, Davis delivers a gripping account of young Brierley’s Homeric odyssey across India, during which time he’s played by extraordinary newcomer Sunny Pawar. These scenes could anchor an entire movie on their own even without the 20-year time jump that follows them. Pawar has a naturalism that would feel at home in a classic neorealist drama, and Davis compliments that skill with a complex environment that follows the child through one perilous location to another. Shot by veteran cinematographer Greig Fraser (“Zero Dark Thirty”), “Lion” moves from a claustrophobic train car to crowded streets and dark tunnels as it builds a sense of desperation around young Saroo’s conundrum.

As an ambitious young adult hoping to study hotel management, he quickly falls for a doe-eyed American student played by Rooney Mara, cast with a thankless part that calls for her to coach Saroo into confessing his desire to research his past. Their underdeveloped romance epitomizes the listless quality of the narrative after it establishes Saroo’s newfound mission.

But even as it drags through a pedestrian middle section, “Lion” remains a cut above the kind of sturdy middlebrow drama its premise calls to mind by doubling down on Patel’s performance. As he grows more disheveled and introverted, he’s infuriated and guilt-ridden by the privilege surrounding him and haunted by fleeting memories of his past, Patel delivers his most intricate performance since “Slumdog Millionaire,” to which “Lion” bears a notable comparison.

Both movies are based on true stories about Indian children from poor backgrounds who endure transformative experiences that catapult them to new worlds, but here Patel must convey a more complex transition — trapped between the desperation of his childhood and the sanctuary of his upper middle class adulthood, Saroo internalizes a complex process of confronting his true identity. His struggle reaches its apex in a bleak encounter with his adopted brother (Arka Das), whose moody personality makes him a burden for the boys’ parents as Saroo comes to grasp that none of them are related, anyway. It’s here that Kidman lands a few emotionally resonant moments, as her affection for her children and desire to provide them with happy lives complicates Saroo’s relationship to his old home.

Just when it begins to stumble into a cycle of shrill melodrama, “Lion” regains its initial intrigue as a detective story. Saroo spends late nights sifting through digital maps and crunching numbers to determine his origins, bringing fresh context to the engaging moments that open the film. It’s no secret that the effort pays off, and “Lion” makes the trip worthwhile not only for mother and son but for the audience as well. The reunion earns its tears by arriving at the end of a strenuous journey that begins by accident and concludes only through sheer determination. It’s the rare sappy finale that doesn’t force the feels; they’re built into the drama so well that Davis only needs to connect the dots and let the material do the rest.

“Lion” premiered at the 2016 Toronto International Film Festival. The Weinstein Company opens it theatrically November 25.

THIS ARTICLE IS RELATED TO: Film and tagged Lion, Nicole Kidman, Reviews,TIFF 2016