What can we do if people treat us inhumanely? This is the question posed by Jonathan Salt’s new play, and the answer he finds is: we must be more than human. This biopic of Janusz Korczak, a Polish Jewish doctor, writer and head of a Jewish orphanage, shows a man striving to be more than human, showing immense compassion and respect for others in the face of the Nazi brutality, on the night before he and the children in his care were sent to the death camps.

The setting is his room in the Warsaw Ghetto, slightly confusingly conjured up by a set that’s all wooden slats and acute angles. On pitiful rations and without medical supplies, he’s trying to keep the shattered pieces of life at the orphanage’s temporary home in some kind of coherent whole. Outside, gunshots ring out, while his solitude is continually interrupted by children coming to him with their problems, which he takes as seriously as the events beyond the orphanage’s walls.

Jonathan Salt’s evocation of Korczak has a real charm to it, as he alternates between philosopher and child, playing trains on the floor, while his script finds some fascinating details in this true story. His reminisces of a bourgeois childhood are interspersed with detail about his obsessive interest in the children’s digestion, about new additions to the tooth castle in the attic, creating a picture of a fascinating man dedicated to his work and to others.

As a piece of theatre, though, this one man show is occasionally lacking. There are some touching moments, such as his placing of a small jumper on a medical screen to represent a child up a tree, scared. Other moments of physical theatre fall flat; in particular, his handkerchief fails to take flight as a remembered canary in a moment that would benefit from some closer direction. A lack of technical skill also damages his interactions with the children; the risk of talking to invisible people is coming across as a raving madman, and his roving line of vision as he interacts with his charges makes it hard to imagine where on stage they are, how old they are, or even whether they’ve left. A really notable failing is in the light and sound design – lighting states switch, rather than fade, abruptly, for no clear reason, while the sound is tinny and unconvincing. It might be advisable to scrap the sound effects of children playing altogether; unnatural and obtrusive, they emphasise the artificiality of the stage setting, rather than evoking the busy orphanage, while Korczak’s disturbed night’s sleep would be better unadorned with red light and bizarre noises.

Alone in his room, Korczak asks, “Would this happen if children were in charge? Could children be so cruel?” For anyone who has seen Lord of the Flies, the answer would be more complex than the unequivocal “no” given by his boundless faith in human nature, in his longing to show the children that the world can be a fair, just and loving place. Jonathan Salt’s play is a fascinating portrayal of a truly interesting man in horrendous times – if, occasionally, it feels more like education than a play, it is a subject that it is well worth being educated on.

Confessions of a Butterfly is playing at the Lion and the Unicorn Theatre until 29 September. For more information and tickets please see the Lion and the Unicorn website.