The Enlightenment: that celebrated period in Western civilisation when reason, scientific thinking and analysis, and a belief in the rights of the individual, would challenge and supplant mediaeval world-views mired in superstition, fear and institutional authority.
But can there be enlightenment in a situation so terrible that there is no logical reasoning nor cool analysis to help attain answers to questions nobody wants to confront: my child is missing so where is he and what may have happened to him?
Before she joined the Downton Abbey writers' desk, Shelagh Stephenson won plaudits for her plays, which are family dramas - and sometimes comedies - of an altogether knottier kind than the British period television series. They've been described as intense and intelligent yet shot through with humour.
Although Enlightenment is an earlier work - Stephenson wrote it in 2005 - global terrorism means its premise remains sadly relevant. Adam has gone backpacking and the last his upper middle-class academic parents, Lia (Rachel Nash) and Nick (Stephen Lovatt), hear from him is a vague email mentioning he might go to Jakarta.