Available on DVD: “Oranges and Sunshine”

In the quietly wrenching Oranges and Sunshine, Emily Watson portrays Margaret Humphreys, an intrepid social worker from Nottingham, England, who exposed shameful national crimes. As recently as 1967, but especially in the 1940s and ’50s, as many as 130,000 children were removed from orphanages and group homes in Britain and deported to various locations in the Commonwealth, particularly western Australia. One deportee, now grown up, recalls being told at the age of 10 that he was being sent to a sunny paradise where he could pick oranges off trees.

Instead of lotus land, many found themselves virtually enslaved and forced into hard labor in institutions where they endured physical cruelty and sexual abuse. One of the worst was the remote Bindoon Boys Town, a hellish place presided over by the Catholic Christian Brothers, where many boys were raped.

The victims, who were told that their parents were dead, had no recourse but to endure until they were old enough to leave. Many were taken from parents, mainly unwed mothers temporarily deemed unfit. When they later searched for their offspring in orphanages, they were told their children had been placed for adoption in better homes.

If the film, adapted from Humphreys’s 1994 book, Empty Cradles, tells a true-life horror story, it refrains from exploiting that story for cheap shock. As directed by Jim Loach, the son of the great social realist filmmaker Ken Loach, it keeps its eye on the long view and maintains a steady, melancholic tone that conveys a resolute moral outrage.

There are two scenes in which Humphreys’s safety is threatened, but the hostility she encounters in her investigations isn’t overamplified. Nor is Watson’s Margaret a charismatic Joan of Arc leading a righteous brigade into the bowels of hell.

Margaret, who is assisted by her husband, Merv (Richard Dillane), is a fragile lone wolf who sacrifices the comforts of family life to pursue her work and eventually crumbles under the stress yet keeps on going. In Watson’s powerfully understated performance there are occasional speeches but no stentorian orations. Her cause is the only thing that matters. The awful fact of British and Australian complicity speaks for itself.

The scenes of reunions between long-separated siblings and between parents and their vanished children are all the more touching for their restraint. There is abundant emotion in the film, but it isn’t allowed to sidetrack Margaret’s quest for answers or to achieve whatever justice can be salvaged. In its quietude Oranges and Sunshine is the opposite of the recent film The Whistleblower, a devastating, high-pitched exposé of human trafficking involving United Nations workers in postwar Bosnia.

This film presents a chilling portrait of bureaucratic stonewalling and denial as Margaret presents her evidence to politicians who meet her accusations with indifference and skepticism, express only a vague regret and assume no responsibility. When she eventually faces a group of clergymen at Bindoon, she is met with absolute silence.

The story begins in 1986, when Margaret, a social worker for the Nottingham County Council, is approached by Charlotte (Federay Holmes), an Australian who pleads, "I want to find out who I am." Charlotte recalls that when she was 4, she was placed alone on a boat bound for Australia after being told her mother had died. Margaret, digging through official records, finds Charlotte’s mother, and they eventually reunite.

Margaret travels to Perth with a British woman named Nicky (Lorraine Ashbourne) in search of her long-lost brother Jack (Hugo Weaving), whom she finds. In Australia, Margaret discovers a loosely knit group of deportees, now adults, who voice a plaintive longing to know who they really are. When Margaret publicizes her search in newspapers and on television, victims flock to her, but she also finds herself increasingly under attack. The film devotes special attention to Len (David Wenham), a high-strung former resident of Bindoon who persuades her to accompany him on a visit to the place.

Rona Munro’s screenplay for Oranges and Sunshine is unnecessarily flighty. As the story ricochets between Britain and Australia, the film often loses track of time and becomes fragmented as it struggles to integrate too many subplots. What holds it together is Watson’s calm, sturdy performance.

Early in her crusade Humphreys established the Child Migrants Trust. But it wasn’t until 2009, 23 years after she began her search, that the Australian government formally apologized for the forced deportation of child migrants; the British government followed suit in 2010.