Isn't it funny how your life sometimes develops a strange theme for a week?

My theme for the past week has been "suspect nuns".

Last Sunday I found myself among a lot of unholy-looking mother superiors at Brighton's Theatre Royal.

They were bellowing out the words to Climb Every Mountain and waving plastic edelweiss.

This evening I shall myself be dressed in a wimple and be under suspicion of murder.

The first event was Sing-along-a-Sound of Music, which was a truly highbrow moment in my social calendar.

Just to explain, members of the audience are encouraged to dress up as characters or references from the film and then sing along to all those wonderful Rodgers and Hammerstein classics while the projector rolls.

When a friend of mine first suggested this as a night out, I was a little hesitant, particularly about audience participation.

I hadn't seen the film since childhood and my memories of it were too hazy to feel confident enough to go in costume. My friend, thankfully, agreed with me.

Of course, when we got there, we felt totally out of place among the abundance of nuns, Nazis and several people in brown paper and string (as in "brown paper packages tied up with string" from Julie Andrews' list of favourite things).

There were also a few more-inspired attendees, such as the couple dressed as "warm, woollen mittens" (another of Julie's favourite things) and "the bowing lady".

You needed precise knowledge of the film to understand this reference.

I didn't get it until near the end, when the bowing lady from the audience rushed on to the theatre's stage to join her screen double in accepting third prize in a singing competition. I was tearful with laughter.

Actually, for much of the evening I was mildly anxious. A major part of the time was spent dipping into a small plastic bag we'd each been given and remembering to extract from it an appropriate item (the edelweiss for each time Edelweiss was sung, a piece of material to remind Julie to use her curtains to make clothes for the Von Trapp kids).

I was in a tense state with a party popper for nigh on half an hour in anticipation of the exact moment when Julie Andrews' lips would touch those of Captain Von Trapp - the point at which we were required to pull the string.

Anyway, that was the night of a thousand nuns and I wasn't one of them.

Tonight I will temporarily take up Holy Orders to become Sister Morticia Lewinskaya (the name has a familiar ring to it).

The occasion is one of those murder-mystery dinner parties in which you all turn up in character and then have to pay attention to the unfolding plot to nail the killer - who could be yourself.

The last time my husband and I went to one of the evenings we'd totally lost the plot (in all senses) before the end of the main course.

I've already decided that if I start to feel panicky this evening, I'll stand on my chair and launch into "The hills are alive . . ."