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.
Then, for five months, nothing. Their fears are heightened by his possible proximity to bombings in the Indonesian capital. Having searched for him and exhausted all logical pathways, they turn to a dubious psychic (Catherine Wilkin) and, reluctantly, to an ambitious television reporter (Anna Jullienne) introduced to them by Lia's father (David Aston). It seems their prayers are answered when a boy (Jordon Mooney) claiming to be their son arrives from Thailand but is he whom he says he is?
True to the historical period the play takes its name from, it's shot through with references to scientific theories, physics and metaphysics. Director Andrew Foster is quick to reassure one doesn't have to be a boffin to become engrossed as the play deals with ideas about hope amid fear, reason and rationality and the outcomes of parental grief.
Lovatt and Nash agree being parents themselves adds to their understanding of their characters' sense of helplessness but determination to find out what has happened to their son.
"Being a parent and experiencing that depth of love that you feel for your children is quite significant for me as an actor," says Nash. "One of my daughters is overseas but that's not what I want to draw upon in terms of this character."
However, she has spent some years working as a funeral director and says her experiences assisting the grieving help her to understand some of Lia's emotions.
"It's amazing work, very privileged work, but it's not easy. Grief is often very raw; it's certainly not all polite sobbing by the graveside."
Lovatt says Lia and Nick are close, but there are fissures in their relationship which the circumstances heighten. Nick is Adam's stepfather and Lovatt believes Stephenson has written the character as such to explore ideas about attachment. He says it's an emotional thriller with two leads who are highly recognisable characters helped by dialogue that is "robust and muscular", yet very naturalistic. That contrasts with a set which, as specified by the playwright, is anything but.
"The characters are extremely sympathetic and I'm sure there will be times when the audience thinks, 'That could be me saying that'. It's a very minimalist set and I think that throws the naturalism of the characters into relief.
"It's about more than a couple dealing with the loss of a child; it's about the ramifications of what it does to them, about how they find their own enlightenment and about the human condition. It has all kinds of echoes for everyone; it's a play I would really love to see."
May 28-June 20