Tertius is a master of disguise. It's not unusual for me to sense a presence while I'm working and turn around from my desk to be startled by a three-foot-tall Darth Vader or a poker-faced knight in chain mail staring at me. (I have got to move my desk so I don't have my back to the door.)
This evening, I was in the kitchen, making a shepherd's pie for dinner (I use lots of cumin) when there was a tap on my back. I turn. Tertius is wearing a pair of those plastic "Groucho" glasses, with eyebrows and fake nose, and a fluorescent-yellow Zapata moustache and zig-zag beard cut from several Post-It notes.
"Just a moment," he says, and heads off to his bedroom. A minute later, he reappears, having added a MacDonald-tartan tam o'shanter, pulled down to his ears.
"I'm French," he announces.
But of course you are.