I'm walking around looking for where the batteries have been moved to, when I hear a familiar voice.
"Look at this!" says a man who is almost completely hidden behind a fake Christmas tree.
I'm so mindlessly obedient that I do as he tells me. Oh, Christ, it's Richard Levinson, the man who says he's too refined to live on a council estate.
"This'd put a smile on Santa's face, wouldn't it?" he says.
He's got such a carrying voice that everyone in the shop is looking in our direction by now. For one very long moment, I am convinced that Richard is talking to me, and am paralysed by horror. Has it really come to this?
I look down at the floor, and try to will myself to disappear into it. Which, as usual, doesn't work. When I look up again, Richard's still holding the packet and shaking it at everyone who walks past.
"Ooh - if I was a few years younger, I'd buy one myself," says an elderly woman, whose voice I also recognise. It's Miss Harpenden, of all people. She of the flying rat fame.
To his credit, Richard shudders but doesn't actually reply to Miss H's horrible suggestion. He's too busy waving the "Sexy Santa" set at another woman - a younger one, who seems to be trying very hard to ignore him.
By now, I'm feeling quite panicky. What the hell have I walked into? It's like a re-make of One Flew Over The Cuckoo's Nest. All we need now are Miss Chambers and Mr Beales and we'll have the full set. Of people who aren't the full set, if you see what I mean.
"For God's sake, put that down. Now. If you think I'm wearing that, you've got another bloody think coming."
So this must be Richard's elusive fiancee, the one with the nasty skin condition. I can't say I blame her for being so pissed off. Even without rampant sores, it'd be a challenge to look alluring in a red polyester bra and knickers, bizarrely topped off with fuzzy red reindeer antlers that light up. Maybe the lack of a hat is why the set is so cheap.
The woman starts to walk away but, by now, half the population of Northwick seems to be getting involved. Some people are so nosy.
"Ah, go on, love," says another man. "Make the lad's Christmas."
This receives no response whatsoever, so then Richard, who never knows when to keep quiet, says,
"Forget Christmas, I was thinking about tonight."
His fiancee looks him up and down, very slowly, then says, "You can fuck off."
With that, she abandons her basket of pan scourers and perfumed candles, and walks out of the shop. Several women start to clap, then stop as suddenly as they started.
Richard looks at his audience, makes one of those "what can you do?" gestures with his hands, then puts the Santa set back on the shelf. Although he tries to look as if he's strolling when he leaves the shop, everyone can tell that he's running.
When I get back to work, and tell Greg about my lunchtime shopping experience, I realise that, after all that, I've forgotten to buy the bloody batteries.
"Don't worry," he says. "I'm going to get a sandwich so I'll pop up there and get them for you. Then I can check the shop's not running regular day-trips from the loony bin."
When he returns, I'm busy talking to Joan, who's hassling me to choose what I want from the Christmas lunch menu of the local pub. I really don't think smearing salmon in chestnut pesto counts as festive, and everything else looks bloody horrible, but Joan's insistent that I have to choose something.
"This combined office 'do' might be the only Christmas lunch you get for work," she says. "If Andrew finds a reason to cancel your proper one again."
"Oh, I don't think he will this year," I say. "Vicky's already bought a new dress for it."
Joan pulls a face that is worth a hundred words - even better than her usual imitation of the bus driver from South Park - then advises me to order one of everything, on the grounds that The Boss will eat anything anyone else doesn't want, and probably some of what they do.
By this time, I've forgotten to ask what else was in the enormous Pound-Den carrier bag Greg was carrying, and I remain in the dark until we're locking up at the end of the day, when he passes it to me.
"Here's your batteries, Mol," he says. "Pay me back tomorrow."
"What's this?" I say, pulling out a large present encased in the tackiest Christmas gift wrap you're ever seen. Santa's nose is redder than The Boss's and alarmingly phallic.
"Just a little early Christmas or birthday present for Max," he says. "I hope it fits you."
"Oh, for God's sake, Greg. Tell me you haven't?" I say, but when I try to give the parcel back to him, he just taps his nose, and says,
"Keep an open mind, Mol. Might render those batteries redundant."
Honestly, how much humiliation can women be expected to take? And, anyway, I bet you need batteries for glowing antlers.