Romance, intrigue and a £10m horse
Ah, young love. Girl meets boy. Boy meets girl. Boy acquires world's most expensive horse. Girl and boy battle for Olympic glory.
The pair, both 26, are the two strongest candidates for Olympic gold in London next year. They are also former lovers.
Until late last year, they faced another rival in the form of Totilas, the Justin Bieber of the equestrian world. Totilas is a prancing black stallion with moves unlike any other, a genuine equine superstar who helped the Dutch team to two world titles in 2010.
But then the Germans bought Totilas - for a fee believed to be upwards of £10m, making the horse as valuable as a Premier League footballer - and handed Rath the reins. Great news for him, less so for his British ex.
"Totilas has been amazing for the sport, he's a phenomenon," says Bechtolsheimer as we tour her luxurious yard in Gloucestershire, which has been nicknamed the 'Hilton for horses'.
Her surname may not strike you as British. Her family -who make appearances in both the Sunday Times and Forbes rich lists - hail from Germany but she moved to Britain as a toddler and, in her father's words, "sounds like, competes and thinks as a Brit". Now, Germany is her main Olympic rival.
"Everyone wants to see Totilas," she continues. "He has so much extravagance and he broke all records in a way no other horse before has done.
Totilas makes one of his first outings with Matthias Rath. Photo: Getty Images
"Other than racing, no horse has gone for that amount of money. It's just not relative to anything else. Before, if a horse was sold for £2m it was like 'Oh, my God'. Totilas? That's a joke."
Watching your ex arm themselves with the most potent weapon in your sport may not be a very funny joke, ahead of your home Olympics.
However, it might be the best thing that could have happened to Bechtolsheimer's chances.
She and her horse, Alf, have been training together for years. London will be 16-year-old Alf's last shot at an Olympics.
By contrast, young upstart Totilas (now 11) and Rath have only a year to get to know each other, in a sport founded on the subtleties of communication between horse and rider.
"Totilas was my biggest rival but now he has a new rider, we'll see if he stays that way," she says.
"It depends how Matthias gets on with him: how he copes with the horse, and the pressure. I'm sure he's having a good time, but he's having to deal with a lot of pressure."
That's because as far as many people are concerned, the Germans have gone out and bought themselves an Olympic gold medal - spending more money in the process than the entire British boxing team, for example, has received in funding for London 2012. Rath can only live up to expectation by winning gold, or fail.
When I speak to the horse's new co-owner, former Olympic dressage champion Ann-Kathrin Linsenhoff, she refuses to confirm the sum paid. Everyone else in the sport believes it is well into eight figures.
"For me, Totilas is not about money, it is a heart thing," says the flamboyant Linsenhoff at the new home of the 'wunderpferd' - a stables near Frankfurt.
"Totilas is the best horse I have ever seen. You know how there are people who fill up a room? There is only one horse who fills up a room, and it's Totilas. He's a winner. He wants to win.
Laura Bechtolsheimer with Alf, preparing to take on Totilas for Olympic gold. Photo: Getty Images
"People say we have bought an Olympic medal but even if you have the best horse, it won't win gold if you can't ride it."
So no pressure on Rath, then, previously ranked about 10th in the world (Bechtolsheimer has hovered around second behind Dutchman Edward Gal, former rider of Totilas).
Rath tells me: "I don't think about how much he cost. If I thought about that every day, it wouldn't work.
"When we bought him, we came into his stable and normally you go to see a horse and you look at him. This time it was the other way around: Totilas was looking at us. He really checked us out. Now, it's a question of how well I come together with him."
Bechtolsheimer and Rath, or Alf and Totilas if you like, have now begun to compete against each other. So far, honours are almost even.
"We're still quite good friends although I haven't spoken to him recently," says Bechtolsheimer.
"I did speak to him when he'd just started riding Totilas. He said he was very excited and the horse was incredible to ride."
Rath adds: "She said I shouldn't be too stressed about it, that I should take my time. She knows me quite well; she knows how I react, it was a good talk."
How, though, does Rath think she will feel if he and Totilas deprive her of home Olympic gold next year?
"I'm quite sure she will forgive me."
You can see more from Laura Bechtolsheimer, Matthias Rath and Totilas on British Olympic Dreams, on BBC One from 1315 BST on Saturday, 18 June.