Then, this evening, after a browse around the half-price ticket booth in Leicester Square, I decided that the only thing that appealed was a Royal Shakespeare Company Spanish season play House of Desires. (By the way if you are visiting don't be fooled - the proper ticket place is a standalone building in the middle of the square; don't go to any of the joints located in various rows of shops around it or you'll pay for the mistake.)
I had no idea what the play was, but you seldom go wrong with the RSC, so I trotted down to the theatre and picked up a £10 seat there. (This is often cheaper than even the legitimate ticket booth.)
Then, what do you know, I was reading the programme over my neighbour's shoulder, and I realised this was a play by the said Sister.
It is on one level a madcap farce - a variation on the English drawing room scamper with mistaken identities and hidden people overhearing conversations all over the place - and frequently genuinely funny, if sometimes a bit obvious - but it is also a scathing comment on the Sister's society, and particularly the honour culture that weighed so heavily on women.
This becomes particularly evident at the end of the second act, in which the men are concerned not with the fate of their supposedly beloved daughters and sisters, but only with their own honour, and they can't get them married off under "shotgun wedding" conditions fast enough.
Not that the women are saints by any means. The Sister appears to have identified with Doña Leonor, a beautiful learned, if horribly vain girl - the staging has the nun watching the initial action before stripping off to reveal her identity. (Although I doubt that can have been so in the original script.)