Film-maker Gabrielle Brady tells a powerful and moving story from inside Australia’s Guantánamo: Christmas Island, the country’s offshore territory near Java, where asylum seekers and boat people are warehoused in grim conditions that the authorities are in no hurry to conceal – because of the deterrent factor, an important part of the government’s anti-migrant crackdown since 2013. (The similar Manus Island facility has now been closed but the equally grisly Nauru is still in business.)

Poh Lin Lee is a torture and trauma counsellor permitted to give therapy to detainees, who are terrifyingly scarred mentally. These sessions have been reconstructed as filming current detainees was not possible; conversations take place with migrants who have been released. Brady could perhaps have made that point clearer (there is a self-evidently imagined sequence at the beginning depicting an escape), but the pure emotional agony of their testimony is real enough, and the sequence where an Afghan man talks about how he was separated from his elderly mother is devastating: “It’s a kind of hell here … Hell is where you see your family suffering and you can’t do anything.”

The awful truth is that the detainees are getting just as much trauma here as in the place they left or on their terrible sea journey. Lee’s patients often simply never show up for their sessions, having been moved to another prison camp, and Lee is told nothing. However brutal, this film is also unexpectedly beautiful, because of the almost dreamlike shots of the red crabs that swarm over the island, like the unquiet spirits of prisoners.

The title comes from the practice of the island’s Malay Chinese community, who pay homage to the souls of their forebears: indentured labourers brought over a century ago in comparably cruel circumstances. A fierce, valuable, compassionate film.