lightning strikes. We stopped somewhere on the way to Royston and the driver came on the intercom and said “Sorry for the delay, we're having some technical problems. I'm going to try rebooting the train.” - and indeed, the motors stopped, the lights went out. Shortly afterward the lights came on again, then the destination display panel briefly read "BRB Class 465".
Oh, and if anybody wants to eat Korean food in London, I can recommend Ran on Great Marlborough Street. Very tasty bulgogi and spiced belly-pork; barbequed on a gas-ring-with-charcoal for you at your table. The rest of the meal was also good, and the prices weren't too bad (£50 for a good amount for two with a bottle of wine).