At nine o'clock sharp on Tuesday evening my mother received another demand from the blackmailer. The three residents of Kauri House were suffering through another unhappy dinner around the kitchen table when the telephone rang. Both my mother and stepfather jumped, and then they looked at each other.

"Nine o'clock," my stepfather said. "He always calls at exactly nine o'clock."

The phone continued to ring. Neither of them seemed very keen to answer it, so I stood up and started to move over towards it.

"No," my mother screamed, leaping to her feet. "I'll get it."

She pushed past me and grabbed the receiver.

"Hello," she said tentatively into the phone. "Yes, this is Mrs. Kauri."

I was standing right next to her, and I tried to hear what the person at the other end was saying, but he or she was speaking too softly.

My mother listened for less than a minute.

"Yes. I understand," my mother said finally. She placed the phone back in its cradle. "Scientific at Newbury, on Saturday."

"To lose?" I asked.

She nodded. "In the Game Spirit Steeplechase."

She walked like a zombie back to her chair and sat down heavily.

I picked up the phone and dialed 1471, the code to find the number of the last caller.

"Sorry," said a computerized female voice, "the caller withheld their number."

I hadn't expected anything else, but it had been worth a try. I wondered if the phone company might be able to give me the number, but that, I was sure, would involve explaining why I needed it. I also thought it highly unlikely that the blackmailer had been using his own phone or a number that was traceable back to him.

"What chance would you expect Scientific to have anyway?" I asked.

"Fairly good," she said. "He's really only a novice, and this race is a considerable step up in class, but I think he's ready for it." Her shoulders slumped. "But it's not bloody fair on the horse. If I make him ill again, it may ruin him forever. He'll always associate racing with being ill."

"Would he really remember?" I asked.

"Oh yes," she said. "Lots of my good chasers over the years have been hopeless at home only to run like the wind on a racetrack because they liked it there. One I had years ago, a chestnut called Butterfield, he only ran well at Sandown." She smiled, remembering. "Old boy loved Sandown. I thought it was to do with right-handed tracks, but he wouldn't go at Kempton. It had to be Sandown. He definitely remembered."

I could see a glimpse of why my mother was such a good trainer. She adored her horses, and she spoke of Butterfield as an individual, and with real affection.

"But Scientific is not the odds-on sure thing that Pharmacist was meant to be at Cheltenham last week?"

"No," she said. "There's another very good chaser in the race, Sovereign Owner. He'll probably start favorite, although I really think we could beat him, especially if it rains a bit more before Saturday. And Newark Hall may run in the race as well. He's one of Ewen's, and he should have a reasonable chance."

"Ewen?" I asked.

"Ewen Yorke," she said. "Trains in the village. Has some really good horses this year. The up-and-coming young opposition."

From her tone, I concluded that Ewen Yorke was more of a threat to her position as top dog in Lambourn than she was happy with.

"So Scientific is far from a dead cert?" I said.

"He should win," she stressed again. "Unless he crossfires."

"'Crossfires'?" I asked. "What's that?"

"It's when a horse canters and leads with a different leg in front than he does at the rear," she explained.

"OK," I said slowly, none the wiser. "And does Scientific do that?"

"Sometimes. Unusually he tends to canter between his walk and gallop," she said. "And if he crossfires, he can cut into himself, hitting his front leg with his hind hoof. But he hasn't done it recently. Not for ages."

"OK," I said again. "So even supposing that Scientific doesn't crossfire, no one would be vastly surprised if he didn't win."

"No," she agreed. "It would be disappointing but no surprise."

"So," I said, "after that call from our friend just now, all we have to do is ensure he doesn't win on Saturday without making him so ill he gives up on the idea of racing altogether."

She stared at me. "But how?"

"I can think of a number of ways," I said. "How about if he doesn't run in the first place? You could simply not declare him and tell everyone he was lame or something."

"He said the horse had to run," she replied gloomily.

Time to move on to plan B.

"Well, how about a bit of overtraining on Thursday or Friday? Give him too much of a gallop so he's worn out on Saturday."

"But everyone would know," she said.

"Would they really?" I thought she was being overly worried.

"Oh yes, they would," she said. "There are always people watching the horses work. Some of them are from the media, but most are spotters for the bookmaking firms. They know every horse in Lambourn by sight, and they would see all too easily if I gave Scientific anything more than a gentle pipe-opener on Thursday or Friday."

Was there a plan C?

"Can't you make his saddle slip or something?" I asked.

"The girths will be tightened by the assistant starter just before the race starts."

"But can't you go down to the start and do it yourself and just leave them loose?" Was I clutching at straws?

"But the jockey would fall off," she said.

"At least that would stop him from winning," I said with a smile.

"But he might be injured." She shook her head. "I can't do that."

Plan D?

"How about if you cut through the reins just enough so that they break during the race? If the jockey can't steer, then he surely can't win."

"Tell that to Fred Winter," she said.

"What?"

"Fred Winter," she repeated. "He won the Grand Steeple-Chase de Paris on Mandarin with no steering, way back in the early sixties. The bit broke, which meant he had no brakes, either. He used his legs, pressing on the sides of the horse to keep it on the figure-eight course. It was an absolutely amazing piece of riding."

"And will this Fred Winter be the jockey on Scientific on Saturday?" I asked.

"No, of course not," she said. "He died years ago."

"Well, in that case, don't you think it's a good idea?"

"What?"

"To make the reins break." God, this was hard work.

"But…"

"But what?" I asked.

"I'd be the laughingstock," she said miserably. "Horses from Kauri House Stables don't go to the races with substandard tack."

"Would you rather be laughed at or arrested for tax evasion?"

It was a cruel thing to say, but it did bring the problems she faced into relative order.

"Thomas is right, dear," my stepfather said, somewhat belatedly entering the conversation.

"So it's agreed, then," I said. "We won't subject Scientific to the green-potato-peel treatment, but we will try and arrange for his reins to break during the race. And we take our chances."

"I suppose so," my mother said reluctantly.

"Right," I said positively. "That's the first decision made."

My mother looked up at me. "And what other decisions do you have in mind?"

"Nothing specific as yet," I said. "But I do have some questions."

She looked back at me with doleful eyes. Why did I think she knew the questions wouldn't be welcome?

"First," I said, "when is your next Value Added Tax return due?"

"I told you I don't pay VAT," my mother said.

"But the stables must have a VAT registration for the other bills, like the horses' feed, the purchase of tack, and all sorts of other stuff. Don't the race entries attract VAT?"

"Roderick canceled our registration," she said.