Chas has an unusual assignment - to attend an old lady's hundredth birthday party. But Tarot and Mikki sense that something has happened to Chas - who later returns with no memory of what happened at the party - and after it.

Chas, under hypnosis, apparently robbed the post office in the village where the Edgington sisters live. But is he still under some hypnotic power? Meanwhile Tarot has discovered a curious fact about Mathilda Edgington - that she died two years ago!

Tarot, imprisoned in the cellar at Bliss cottage, has found out from the hypnotized Chas that the old ladies plan to kidnap the Commander-in-Chief of British Land Forces, NATO. Mikki escapes to warn the Army authorities, but finds her car surrounded by the old ladies.