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It happens when Andrew Nicholson falls at the second-to-last jump in the cross country. A quick intake of breath followed by a yelp of sheer horror.

"Oh no!" and there's Catriona Williams sitting bolt upright in her wheelchair, hands high above her head in shock, face as white as the snow on the Tararua Ranges. She knows this is disaster for New Zealand's Olympic Equestrian team.

Then, around 60 seconds later, the collection of former horse riders, fellow fundraisers and friends who have gathered round Willams to watch our team battle it out, settle down enough to realise that the worst has not actually happened.

Nicholson gets up and walks away.

If all was fair in this world Catriona Williams would not be here in Masterton, on the Little Avondale thoroughbred stud she runs with her husband, Sam. She would be there, sweating it out in Hong Kong, alongside her friends Nicholson, Mark Todd, Heelan Tompkins and Joe Meyer "who lives just down the road from here". They used to travel together, ride together, compete together. But that was before the accident.

IT happened in spring 2002 at Kihikihi, near Te Awamutu.

"I was on a borrowed mount," says Williams. "Riding a horse as a favour for a friend."

She had been driven to the event by a neighbour. The plan was to pick up their new horse truck at Kihikihi. In fact, it was already there. "I drove that truck 30 metres and parked it under a tree and never drove it again."

The bouncy young woman with the pale blond hair and incredible smile, had already walked over the course. But, in the event, she had no control over what happened.

"The horse was super-careful, super-knowledgeable. He'd jump a little higher, try a little harder ... Anyhow he put two steps in instead of one, hit with his knees, then cartwheeled over the whole fence."

Williams, nicknamed Cat, was 31. She and Sam had been married a year. While the horse scrambled to his feet, her slim body hurtled through the air and landed, head down, in a ditch. There were no other injuries. "I just broke my neck."

It was in the helicopter on the way to Waikato Hospital that she realised she was in trouble.

"It was the most incredible pain, you just can't describe it. I kept asking people to straighten my legs. When they said, 'they are straight' I went 'Oh no, this is not good'. Apparently your legs remember the last position they were in ... "

Three months later, after several days in Hamilton and another week at Christchurch Hospital, Williams was transferred to Burwood Hospital's spinal unit.

"We were all hoping it was temporary," she says. "Then, three or four weeks go by ... "

Christmas came and went too. "On Christmas Day it took us all day to open the Christmas presents. It was quite humbling."

And then, in late summer, after four months of exercises, therapy and adjustment and realising that her future was in a wheelchair, they came home. The break was at the base of her neck between cervical vertebrae C6 and 7.

"That means I can lift my arms above my head," she says. "But it also means that my hands don't work so well."

They arrived home to the old Lockwood with its six steps and doors too narrow for the wheelchair and dozens of mares and foals needing Sam's attention - and although she'd never say it, even this brave, well-connected, talented woman must have sat there and cried.

TODAY, with the help of ACC, they have adapted a 100-year-old farm cottage that was once used as grooms' quarters. Now Williams is within easy wheeling distance of the stables and her black Kia Carnival slips into a covered parking slot precisely outside the back door. The automatic ramp folds down, the wheelchair with the leopard-print bag hitched on the back, whips away from the steering wheel, flicks round and down and Williams, in her jeans and diamante-studded sneakers, is out and putting her chicken and mushroom pies in the oven.

The place is modern, light and spacious. Wide sliding doors and ramps make it easy to get round. Every entrance and exit, including into the shower, is bump-free. There's a robust metal frame between the leather sofas in the sitting room where she forces herself to stand for 30-60 minutes five times a week, and a home gym that doubles as a childrens' playroom.

But although she has been through the various stages of loss: anger, denial, depression and finally acceptance, she has not quite accepted her fate. As she will tell you, they are not giving up. "I have to keep strong so that when they find a cure I'll be able to walk again."

Almost a year after the accident she and Sam joined the Project Walk spinal programme in San Diego clinic in Los Angeles. There, after months of exercises she regained strength in her stomach muscles, hands and fingers.

She emerged strong and determined. For several years she commented at the country's major equestrian events. Although she and Sam have not had children yet, she knows that it is possible and they live in hope. In the meantime they have Billy, the chocolate labrador who likes to pull Williams' wheelchair along, and nine godchildren between them. There is a cool, much-used tree fort between the kitchen window and the foaling paddock.

Williams is a working partner in the 250-acre stud which has been in Sam's family for three generations. His dad, Buzz, and Buzz's wife, Susie, still live on the property, helping manage between 140 and 300 brood mares and foals, yearlings and two-year-olds, plus the stud's two stallions, Towkay and Zed and the odd racehorse needing a spell.

During the foaling season Sam is called out most nights. As Williams explains, "When the mares drop, Sam gets a call and he goes over [to the foaling paddock] to help pull".

"We breed champions, that's the plan."

Her study is lined with photos. At Burleigh and Badminton in England on Win For Me, where she came 15th. By 2001 she was a Grand Prix showjumper and a four-star eventer who had represented New Zealand in both disciplines.

Looking at the photos of her past triumphs doesn't make her sad: "it makes me feel like it really happened!".

As anyone who rides will tell you, it is far safer on a horse than off and Williams is not as confident around horses as she was. "They don't like the chair and also I feel vulnerable, because I can't move fast enough." But when we go to the stables her innate ability is obvious. The massive Kalamanda, a broodmare Sam bought from the Aga Khan, gently lips horse nuts from Williams' outstretched palm, carefully avoiding her curled thumb.

HER group of friends is close and energetic. Today, and most days, the place is full of people. Peeps Falloon (widow of former MP John Falloon) and Anna Hiatt, who had planned to go to these Olympics with Williams but cancelled when officials could not confirm a place for the wheelchair, have come here instead.

"We had the tickets and somewhere to stay," says Williams with an unconvincing smile. "In the end we just had to pull out."

Twelve of them, the Jam Tarts, formed themselves into a racing syndicate to run the promising race filly, Eloa. As Williams says, "Sam bred her and it was his idea - partly to give me something horsey to do, to keep me interested." Eloa also turned out to be a money-spinner, winning more than $85,000 in stake money.

But Williams' biggest effort by far is the CatWalk Trust she founded in 2005. "At first they fundraised for me, but then I sat down and said to the girls, 'the only thing that's going to fix my life is to walk again, to be able to dance with Sam again'. And I bet that's what 99 per cent of people in chairs would say.

"Then someone said, 'why don't we do it for research?"'

Which is what happened. Today the CatWalk Trust has a staff of three and patrons including Mark Todd, Richie McCaw and Zara Phillips, the horse-riding daughter of Mark Phillips and Princess Anne. It also has nearly $1 million in the kitty and has already contributed to scientific research studies. "We've pushed to get close to the New Zealand Neurological Foundation," says CatWalk manager, Meg Speirs. "All our funding goes through them, meaning projects are peer-reviewed by the the top scientists in the world."

A grants approval committee, headed by Justice Lowell Goddard, (head of the Independent Police Conduct Authority) assesses applications.

So far CatWalk has helped fund doctors Simon O'Carroll and Tim Woodfield at Auckland and Christchurch Universities in their research into new drugs.

The aim, says Williams, is to find the world's most promising projects. "We don't want to reinvent the wheel. We want to help people walk again." And if that means funding research that will help the new generations of people who sever their spinal cords, that is great too.

Right now Williams' energy is going towards the CatWalk Conquest Freedom Tour - a ride round New Zealand on a motorbike specially adapted for wheelchair users with good hand and torso control.

Williams won't be able to manage the bike herself, but it will give others the chance to enjoy the freedom and power of the world's first high-performance motorbike that can be driven from a wheelchair, the wind in their faces - and ultimately be able to bid for the chance to keep it forever.

The tour starts in Auckland on October 28th and finishes in Christchurch on November 13 with an Up and Away charity dinner where the Conquest bike will be auctioned to the highest bidder.

Hopefully they'll pay plenty. Hopefully the researchers will do their stuff. Because, as Williams says over and over again, what you miss are the little things.

"Dancing with Sam again, having enough grip to pull weeds out of the garden.

"You never dream you're in a chair. After a really great dream you think you're going to leap out of bed.

"And every morning you remember."