A different Christmas.

After a gruelling day in the lab, training Click in the correct way to skin, trim and butcher an estate agent, I did not expect to be faced with a murder mystery. Yet that is exactly what I found.

There is a dead tree in my living room. Not only has it been mercilessly severed at the part that normally joins the ground, the corpse has been draped with shiny fronds, glass balls and little lights. I had to admit that when it came to hiding the evidence, someone had gone about it in entirely the wrong way.

Naturally, such wanton brutality coupled with obvious inexperience led me to suspect Caligula but then he generally eats whatever he kills. He has not been known to decorate corpses before. Click had an alibi, he was with me in the lab. That left only Senga.

Therefore Senga must have stalked and killed this tree all on her own, dragged it indoors and draped it with shiny things. I was impressed at her skill in selecting one of the less dangerous forms of plant life in the swamp, subduing it and manipulating the corpse. I gave it a poke to make sure it was dead, then went to find her. If she is going to kill things, she would be better to restrict her tendencies to things we can eat. It's all very well having a herbicidal maniac around the place but tree soup isn't particularly nutritious.

I thought it best not to open with an accusation, so I casually mentioned the dead tree in the living room and asked if she had noticed it.

"I put it there," she said. "Do you like it?"

I know that tone of voice. It's the one that leaves the last part of the sentence unspoken - 'because if you don't...'

"It's very nice," I said. "Did you kill it yourself?"

"Kill it? No, I bought it. It's plastic so it won't go rotten unlike those stockings you insist on hanging up. Shouldn't you take the feet out of them first?"

"You did what?" I could barely believe my ears. She bought a tree? We are surrounded by free trees and she spent money on one? The woman had evidently lost her mind, or had been beguiled by the shiny things in Old Morag McStench's Shiny Things Shop.

Ah, now that was a likely explanation. The tree was covered in the sort of shiny and pointless things old Morag sells to the gullible, and to those she can snare with her enchantments.

Senga sniffed. "I spent a few coins, that's all. You have plenty. You won't even miss them."

"The reason I have plenty of them is that I don't spend them. Those coins are Father's and when he finds a few missing he's going to be angry enough to invite that banshee over again. Last time he did that I went a week without sleep and ended up stitching my own ears closed until it left."

"Oh don't be silly." Senga pulled an enormous dead bird from the cupboard and slapped it on the table. "Your father has been dead for years. He can't take it with him."

"No, he can't, that's why he's staying here with it." I examined the bird. "What's that for?"

"Tomorrow's dinner."

"No, we are having reindeer." I checked the time. "I hope. I'd better get Caligula and Click ready. It's time to lie in wait on the roof."

Senga laughed. "You won't catch him. You never do. I bet you five gold coins we'll be having turkey tomorrow."

"Four," I said. Oh, I'm certain we can get him this time but haggling just comes naturally.

"Done," she said with that infuriating little smile of hers.

I would have argued further but time had run out. I still had to open the gin traps and set the trip wires and get Click and Caligula onto the roof with crossbows (atomic blasters were disallowed because I am not interested in eating reindeer mince) and hide our footsteps in the snow before Santa arrived.

A dead plastic tree in my living room, a team effort for Santa capture and the risk of losing four gold coins.

Maybe I'm getting old, but Christmas doesn't seem the same any more.