A studied, detailed one-woman production, Eglantyne tells the life story of Eglantyne Jebb – co-founder of the charity Save The Children, and original author of what's now the UN Declaration on the Rights of the Child. In character as Eglantyne, actor Anne Chamberlain takes us back to the early 1900's, talking us through the activist's life story and drawing occasional parallels with her own experiences across the globe in New Zealand.

Eglantyne's story isn't showy or dramatic, but it's a demonstration of what quiet determination can achieve. Her early life is driven by an urge "to know, to know, to know"; not an easy choice in an age when intelligent women earned distrust as much as respect. It's that sense of rationalism which drives her to a philosophy of "practical morality", sending destitute children not prayers, but cans of milk. By the end of the play she is travelling the world – overseeing aid projects, tapping up the Pope, and driving a modern vision of fund-raising through innovations such as cinema.

Chamberlain is convincing as the slightly proper, slightly fearsome Eglantyne, whose failing health means she's forever "hurrying up to do something before I die". Some nice metaphors are woven through her self-penned script, often calling back to Eglantyne's Shropshire upbringing and Chamberlain's own early life. And there are moments of humour, largely driven by Eglantyne's no-nonsense audacity; when she was banned from campaigning in the open air, she simply hired the Royal Albert Hall.

It's ironic, then, that this production doesn't display quite the same sense of adventure. It's a very straightforward, largely chronological telling of Eglantyne's life – more described than shown, like an autobiography being read aloud. There's no doubt that it's a well-researched play, but I wondered at times what it gave me that I wouldn't have got from an equally well-researched book.

And Eglantyne's stiff-upper-lip persona, skating quickly over the numerous shadows that fall across her life, doesn't offer Chamberlain many opportunities to portray the emotion behind the mask. One scene – a lengthy exchange of letters with a would-be lover – does show some heart, a rise and fall of the spirit. But in general it's difficult to see your way past Eglantyne's defences, and so the hard knocks she takes in her personal life don't have the impact they could do.

Eglantyne's story is well worth telling, and Chamberlain tells it well. For me, it doesn't quite add up to a rounded piece of theatre, but it's an enjoyable historical talk – throwing light on the origins of a well-known charity, and giving a truly extraordinary woman the recognition she deserves.