It's a true story tailor made for a Hollywood movie, with all the elements both award winners and plot-heavy adventure tales need – fractured family, a long journey, tear-jerking reunions and detective work.

Lion wields all these and more pretty effortlessly, although it's probably the real story as much as the script that makes it successful at doing so. But it also puts some accomplished actors together with beginners (little Sunny Pawar in particular) who don't have nearly as much experience but nevertheless turn in astonishing performances.

When little Saroo (Pawar) gets separated from his loving older brother Guddu (Abhishek Bharate) on an abandoned train station late one night, he ends up locked in a freight train and taken all the way across India where he finds himself in Calcutta, six years old and not knowing where he is or even speaking the language.

The wily but frightened boy tries to get by on the streets, unsure how he'll get back to a home he has no idea how to reach and making it through several terrifying scrapes with both the cops and what appears to be a child trafficking ring.

He finally finds himself in an orphanage where he thinks be might be okay, but no sooner settles in and makes a friend than he's whisked off to Hobart to be adopted by loving parents Sue (Nicole Kidman) and John (David Wenham).

As the bewildered Saroo gradually looks like he'll get used to his new life, we cut to him in his late 20s (Dev Patel), happy with his adopted parents, enjoying his life and preparing to leave for hospitality college in Melbourne.

But it's while he's at a party with friends and other students that something quite innocuous (a fried dessert, in this case) sparks a memory in him, opens a floodgate, and suddenly Saroo's life is transformed as memories of his brother, birth mother and life as a little boy start to flood back, a part of his past he'd forgotten.

He becomes obsessed with finding home, ostracising his girlfriend (Rooney Mara in a pretty superfluous role designed only to highlight the extent of Saroo's obsession as he throws her aside to pursue it), letting his studies suffer and making his parents worry about him. There's a lot of him using a new tool called Google Earth – only recently released as the movie takes place.

In fact there's so much of it you worry for awhile that it's going to be a mystery story complete with the lazy 'computer investigation' scenes that infect so many thrillers. He even has charts and photographs connected with string on his wall like a police detective tracking a killer, foregoing food and sleep as he sinks further into mania over it.

But it's all leading to a gut-punch of a scene near the end when Saroo starts to see familiar terrain on his computer screen, intercut with memories of him walking through it near his home as a little boy, leading him – via his laptop – right to his old front door. If you've ever been hit with a particularly potent memory from a time decades before you didn't think you remembered anything about, it's a very powerful concept.

As the grown up Saroo, Patel is fine if a little bit forced. Kidman commands the screen with her performance in a pretty slight role, but for at least the first half, all the attention – literally and otherwise – is on Panar.