On Tuesday night, Fox's Keen Eddie — the tale of an NYPD-turned-Scotland Yard detective — debuted to humble ratings. The show stars Mark Valley (Pasadena, Days of Our Lives) as Eddie Arlette, with blonde Brit Sienna Miller as his feisty flatmate, Fiona Bickerton. We couldn't help but notice the irony of her past guest spot on The American Embassy — Fox's first unsuccessful attempt at a quirky American-in-London show.

"I was the receptionist in the hairdresser's!" the 20-year-old recalls of her AE moment. "I was called 'Babe in Hairdresser' in the credits. I've also done a couple of low-budget English films and a drama for the BBC in London, but Keen Eddie is distinct in terms of what a big thing it is [for me]."

Whatever the Nielsens may say, Miller has a contagious optimism about the cop dramedy. She's especially enthused about head-butting with Valley, since romantic tension obviously is brewing between their characters. "I have a feeling it's going to do well," she muses, "mostly because it was so much fun to make. You can't imagine it not being fun for everyone else!"

Off-screen, Miller and Valley also have an amusing chemistry, constantly trading flirty barbs with each other. She was surprised by the zealous American fan following he enjoys, thanks to Days. "I didn't think Mark was famous when I met him," she says. "He was just this good-looking, all-American jockstrap. Then, I came to New York [with him on business], and all the girls were like, 'Oh my God, it's Jack Deveraux! Can I have my photo taken with you?' And I was like, what?!"