Martin Johnson XV v Jonah Lomu XV: New Zealand's long-suffering hero Jonah Lomu tells Donald McRae about the kidney transplant that has given him genuine hope of being an All Black again.

Today, on opposite sides of the world, two very different rugby matches present a study in stark contrast. It's a simpler and more immediate battle in New Zealand, with the Lions beginning their long-awaited tour this morning against Bay of Plenty in Rotorua - an ancient Maori settlement made mysterious by the white steam curling out of the geysers and springs which zigzag the small North Island town.

But tonight, in mildly suburban Twickenham, a more personal and tragic struggle will transform Martin Johnson's testimonial match, against a Jonah Lomu XV, from a carefree romp into a compelling stage for the huge All Black's return to rugby after his kidney transplant nine months ago.

Lomu's reappearance will be crammed with emotion. For, as recently as last August, the giant icon who once dominated world rugby as completely as Tiger Woods conquered golf, Michael Jordan illuminated basketball and a peak Mike Tyson stalked the boxing ring, could barely lift one shuffling foot in front of the other.

This evening, Lomu will take his first step on a new journey which he believes could culminate in him being picked again for the All Blacks. It marks a radical change in the Lomu saga; the renewed hope instilled by a transplanted kidney taking the place of Nephrotic Syndrome, the renal illness which ruined his rugby career and nearly destroyed his life.

He will run out at Twickenham with the kidney of Grant Kereama, a New Zealand radio personality and close friend, lodged inside his body. Medical advice hardly recommends such arduous activity after a transplant, but Lomu is undaunted.

"August 27th, 2004," he says in his soft voice, "was the day I started my new life. Now here I am - just days away from my comeback. It's not so long since I could hardly walk. So, for me, there's only one game on my mind.

"I understand why there's this huge interest in the Lions' first match - it's a massive tour for everyone back home and over here - but I've got too much going on in my own head. The biggest thing for me is just to get out on that field. Just to do that will be incredible."

Lomu used to be a painfully shy and stuttering man. He seemed far more frightened of talking than of being gang-tackled by four or five hulking rivals. Yet, now, out of terrible adversity, he has become strikingly lucid in describing the worst effects of his illness.

"I'd been sick a long time, but, in the space of a few weeks (early in 2003), I just plummeted. It was like falling off a building and suddenly, bang, you hit the bottom. The first time it happened was on an ordinary day at home. I was taking down some curtains. I took one step, turned around, took another step and then I fell and hit my head hard on the rowing machine.

"I looked up at Fiona, my wife, and she's just standing there - crying. I'm thinking, 'Hang on, wasn't it me that cracked my head?' But, to tell the truth, I didn't know if I'd ever get back up." That terrifying collapse was caused by a complete renal failure after one of Lomu's kidneys had been ravaged by his rare disease. When asked to explain his tangled thoughts then, Lomu reaches for a single word: "Anger . . ."

He pauses and looks away. "There was a whole lot of anger going on. But then something else took over. I had to think rather than just feel angry. How do I take a step? How do I lift my foot off the ground, move it through the air a little bit and then bring it down? I had to teach myself to walk again. Can you imagine that? I was this guy who'd been racing around down there, on that field in 1999, running straight over people, scoring tries, winning games, having fun. And I ended up so sick I couldn't even run past a little baby."

Sitting high up in the stands of an empty Twickenham, almost directly above the corner where he scored one of his many wonder tries, Lomu's memory of the 1999 World Cup seems briefly unbearable. He points silently at the spot where he crashed over the white line after he had run 50 yards at blistering speed, shrugging off four England players who tried to cling on to him. Lomu was unstoppable then - just as he had been four years before.

"I was diagnosed with the illness right before the 1995 World Cup," he remembers. Lomu does not need to evoke the even more unforgettable impact he made in that tournament when, especially during a semi-final rout in which he scored four tries, English tacklers bounced off him like white-winged flies hitting a black wall.

Lomu then, at the age of 20, was a 6ft 5in slab of 19-stone muscle who could run 100 metres in 10.8 seconds. "I was only operating at about 80 per cent of my capacity," he shrugs. "The illness took a lot away from me even then."

The shocking idea that Lomu was playing at 20 per cent less than his full potential leads to an even more troubling thought. His fall has been so great, he must surely be haunted rather than inspired by all that he achieved?

"It actually helped me confront the illness - to see if I could get near that level again. All those long-term goals stayed in my head even when things were at their worst. I was on dialysis for 18 months before the transplant, so it was important I tried to look ahead to days like my comeback this Saturday.

"You need those big goals to drive you on. Otherwise . . . well, you end up in that dark area where you think: 'What do I have to live for . . . ?' I thought about dying whenever I got bad news about other people. Barry White (the singer) died after he'd been on dialysis for years. But the reality hit me hardest when my old girlfriend died from renal failure.

"She had been sick for two years, but she'd never told me the real reason. I got a rude awakening when I heard about her death. That was the darkest day. I was on dialysis when I went to her funeral. I knew then that I could die from this."

After the transplant, Lomu reveals, "I felt a whole lot better because I wasn't on dialysis - that's what zaps you. And then the hard work began. My first goal was a simple one - walk! Me, my wife and our dog would walk in the park. It would be a very slow walk and, afterwards, I'd be mentally more shattered than after a World Cup match. That's the hardest thing: 24/7, you're having to concentrate on simple things like how to walk. But I got better and I started to jog and then run. And now I'm finally ready for rugby."

There is the merest glint of Lomu's past anger when I ask if other players might be unsettled by his return. Will the man once tagged a "monster" or a "freak" now be demeaned further as a "victim"? Will his opponents be tentative in tackling him - out of sympathy rather than fear?

"Let me put it this way," Lomu says bluntly. "If they don't front up and bring their A game against me then they're in trouble. If they've got any uncertainties then they'd better come tell me to my face. I'll tell them I'm stronger than ever."

As to how this might be possible, Lomu reaches for some gym-based statistics which convince him he can complete the most miraculous comeback yet seen in rugby, and force his way back into the All Black squad for the 2007 World Cup.

"I've had lots of guys train with me the last few months and some of them almost pass out because they can't keep up," the 30-year-old insists proudly.

"When you're doing shoulder-shrugs at 225kg and you can do 10 reps four straight times and then go on to do a 400kg leg-press with 10 reps in another series of four, you get an idea of where I'm at. After two hours in the gym I want to push it more, but they can't. They have to go home or they literally collapse."

Surely there is a danger that Lomu could damage himself further in his desperate quest to prove himself? "Nah! I'm close to 100 per cent when you gauge my strength tests. Who knows my limits?"

Lomu has recently signed a contract to play provincial rugby in NewZealand with North Harbour - and if he can come through his Twickenham return, he will resume full-time rugby after flying home next week. Just in time to catch the opening Test of the Lions tour.

"Aw, mate," Lomu laughs, "I think it's going to be three-zip in the Tests."

He soon remembers his old diplomacy.

"Well, I guess I should say, I hope it's 3-0 to us. It could be . . . but I guess the Lions are dreaming of a clean-sweep themselves. It's going to be interesting."

Lomu claims not to feel any regret that, having missed the 2003 World Cup, he will once more be absent from a titanic rugby clash. "I really don't - because I'm not ready for that yet. I'm not eligible for selection anyway. I don't have a contract with the NZRFU any more, and I didn't play Super 12 rugby this year. All I can do is sit back and watch the team I love - the All Blacks."

The All Blacks, however, have moved on. They are embroiled in a different debate - should they pick Joe Rokocoko, one of the many "new Lomus", ahead of the latest batch of flying wings led by Rico Gear and Sitiveni Sivivatu? They do not seem to be pining for their most famous star.

Lomu himself is still hopeful. "I've seen Graham Henry," he says of the All Blacks' pragmatic coach. "I've had a chat with him and he wishes me well in all I want to achieve. He's said to other people that my commitment is deeper than ever. But his best advice is that I should come back when I feel ready.

"Saturday will be the big test. I want to play the full 80 minutes because I've got two years of rust to shake off. And if I can come through that then who knows? If I play well with North Harbour then the next goal is to break into the Super 12s again, and then the All Blacks."

His dramatic recovery sets this morning's tour opener in Rotorua in its proper sporting context. Last week Lomu helped launch a new charity, NeST, which will raise funds for research into Nephrotic Syndrome at Bristol Children's Hospital.

Yet, for all his admirable work off the field, it is difficult to believe that Lomu's most intense rugby ambition will be fulfilled. "All I know," he protests, "is that not so long ago, people said man would never reach the moon. They were wrong. What does impossible mean?"

That philosophical question echoes around a deserted Twickenham. The big man with a new kidney looks up at the afternoon sky, as if in search of the moon or his own seemingly impossible dream. And then he grins and stretches out his hand to give mine a squeeze.

He walks away to have his photograph taken, no longer needing to concentrate on placing one giant foot in front of the other. He laughs out loud instead as if, in his own head, he is already racing towards some invisible try line. Guardian Service