Outside, the roar of cars on the UK's Silverstone track is reaching a crescendo. It's practice day before the high-octane curtain-opener of the World Endurance Championships and the excitement is building with every lap. Indoors, things are differently exciting. I am in a dimly lit mega-trailer with American actor and petrol head Patrick Dempsey, aka Dr Derek Shepherd in the hugely successful medical drama Grey's Anatomy.
He is dressed in racing driver livery. Tanned and twinkly, the odd silver strand in his luxuriant dark hair, rather improbably, he looks even more dishy encased in a fire-retardant suit than he does in surgeon's scrubs.
Dempsey, 49, flew in last night on the red eye from LA after finishing the eleventh season finale of Grey's Anatomy and went straight to the track to compete at the highest level of endurance racing, in comparison to which, F1 is a boy racer's sprint.
"This is a big adventure for me," says Dempsey. He may have been taking those corners at 165 miles an hour, but he still noticed spring and, yes, clocked the lambs. And not just the lambs. The baby lambs. No wonder his nickname is Dr McDreamy. Wow.
In my house, it is Dempsey's turn in Enchanted, playing the straight guy to Amy Adams' fey princess that takes top billing. But for millions worldwide it's Grey's Anatomy that brings on tachycardia in the female population; think a latter day George Clooney in a modern-day ER.
"Grey's Anatomy has been an amazing ride and I'll be forever grateful; it has a real magic to it," he says. "There are so many elements that work well; the cast, the music, the editing. But after three straight months filming, the rest of this year is 100pc focused on driving. At this level you have to be completely committed and I want to see just how good I can get."
It's no coincidence that today Dempsey is wearing a classic Tag Heuer Monaco watch, as immortalised by Steve McQueen in his 1971 film Le Mans. McQueen famously combined motor racing with acting, as indeed did Paul Newman and James Garner. Dempsey is today's embodiment of the Hollywood heartthrob turned serious speed freak.
He's not just keen. He's good. Very good, according to Porsche, who are supporting him and his team Dempsey Proton Racing. They have high hopes; not only that he will lend a little showbiz glitz to proceedings but he stands a realistic chance of making the podium by the time this long haul is over in Bahrain in November.
Dempsey drives like a pro, he trains and works out like one too. His teammates say they have never encountered an amateur racer who is so committed. Today he got into his car for the first time this year and drove. Fast.
"Ah, but not fast enough," he quips, somehow managing to combine an American megawatt smile with an un-American note of self-deprecation. "I missed the pre-season training because of filming, although the crew did a great job of getting me out in time."
Later I learn he made a respectable fifth place at Silverstone. It is clear that he is no sporting dilettante. Dempsey fully intends to pursue two professions.
"I had three or four things offered to me this year and I looked at the scripts and asked myself whether they would move the bar for me in my professional life. The answer was 'No'," he says. "I see no reason why I can't combine acting and racing."
Dempsey, who grew up in Maine, was a ski racer as a youngster and tipped for the Olympics. But life - acting - got in the way and his career took off in a different direction. He was diagnosed with dyslexia at an early age, but learned to adapt by memorising his scripts off by heart. With his first pay cheque he bought a 1963 356 Porsche convertible for under $10,000.
"It was a bargain but my biggest emotional investment," he says. His enthusiasm for the car was such that 10 years ago his future wife Jill, bought him a three-day driving experience and he was hooked; but with rather unforseen consequences. A decade on, with painful irony, his wife is divorcing him, reportedly because of his obsession with motor racing. He refuses to comment.
Dempsey is a father of three; his daughter Tallulah is "14 going on 21" and twins Sullivan and Darby are eight years old. They are, he says, great kids. "Very competitive!" Which is a thing only a competitive parent would deem a compliment.
"Work-life balance is a constant refinement," he says. "It's about perfecting yourself over your lifetime; I tried in the past to bring the kids along but it's difficult now to disrupt their schooling. Being away is a sacrifice, but it's important for them to know that they should follow their dreams like I do."
Mrs Dempsey clearly didn't feel the same way, but for all the teamwork in the pit and camaraderie round the track, driving a car at breakneck speed is a gloriously (perhaps selfishly) solitary pursuit.
"When you go fast, everything slows down and you stop thinking and you're completely present," muses Dempsey. "The challenge is to clear the mind and not allow anything to affect you emotionally; you can't think about the past or the future and that's a great way to live your life. It carries over when I'm not at the track. I enjoy the mental and physical challenge of competing. The truth is in your lap time; the data doesn't lie; you can measure your improvements."
Like Newman and McQueen before him, he needs his adrenaline rush.
"Paul Newman was a great driver and took time to develop himself. If McQueen had been able to race more, he could have been very good," he says. "Those guys are so iconic in so many different ways and to be mentioned in the same sentence is enough of an honour."
An honour, and, I suspect, a challenge. Dr McDreamy has a whole other side to him and he's having the time of his life. But ladies, before you buy your motor-mad husband a driving experience to ignite his passion, remember that passion might not be for you. Caveat Emptor and don't forget to put on your seatbelt. It could be a very bumpy ride.