Rob Morrow and Michelle Nolden, <EM>Numbers</EM> Rob Morrow and Michelle Nolden, Numbers

Let's suppose the total number of viewers itching to see FBI agent Don Eppes (Rob Morrow) on CBS' Numbers (Fridays at 10 pm/ET) hook up with someone for longer than five minutes is greater than the sum of fans who believe TV math has never been sexier and you arrive at... frankly, we don't have the foggiest, but clearly it has something to do with solid ratings for CBS. Averaging 11.5 million viewers this season, Numbers is attracting more people than shows like Crossing Jordan and Law & Order: Criminal Intent. And as the calculating crime fighters on the Friday-night procedural approach the end of Season 2, the show is moving beyond chalkboard theorems to more complex equations, like what happens when you add romance to a series about gangsters and serial killers. And how a working stiff like Don balances job stress and personal affairs.

The results already look promising. In a recent episode, Don's brother, Charlie (David Krumholtz), the one with the math genes and great hair, got together with an old girlfriend. This week, Don has his biggest personal story line yet: An FBI colleague he used to date commits suicide, making Don question the pressures of the job and whether he can ever have a successful relationship. During his investigation of the suicide, he reconnects with Robin Brooks (Michelle Nolden), an assistant U.S. attorney who just happens to look like a supermodel, and ends up in bed with her.

"I've been after the producers to add a personal component," says Morrow, 43, during a break from filming at the Los Angeles Gun Club. "When I was reading up on FBI agents' lives, so many of them reference the fact that they can't carry on relationships. There's a burden this life has on your whole existence, and Don couldn't escape that."

Opening up Don's private world peels the outer layer on a character who until now has had the social life of your typical morgue resident. Show cocreator Cheryl Heuton says, "Don's in his mid- to late thirties and hasn't had a real relationship. Last season he was engaged, but he backed out. On the personal front, he's more of an enigma than anyone on the show."

Morrow himself is much more of an open book. The former star of Northern Exposure has been married for eight years to actress Debbon Ayer and they have a 5-year-old daughter named Tu Morrow. (Yes, you read both those names right.) "Don has all these issues that come from hiding behind his job," Morrow says. "I know what it means to work hard, but I can't imagine sacrificing intimacy for work."

Coincidentally, Morrow and his new Numbers honey already played a married couple  on Showtime's short-lived but critically acclaimed crime drama Street Time. "The only difference was we played felons then," Nolden says. "At least we're on the right side of the law now."

Don's not the only one shacking up. Don and Charlie's dad, played by Judd Hirsch, will soon develop a romantic interest in a female senior-ranking scientist. And even kooky Dr. Larry Fleinhardt (Peter MacNicol) will start to realize that his career anxieties have gotten in the way of his love life.

Although Don and Robin's relationship will cause new problems, Morrow couldn't be happier. "Now that Don's whole private side is opening up, I'd like to see him get into a lot of different messes, and I expect we will," he says. "I want to see where he goes when he disappears emotionally, when he can't handle the closeness of a relationship or an emotion. To see him struggling with those issues would really deepen the experience of watching him."

If our theories are correct, it should also increase Numbers' numbers.

What's the real reason viewers love crime shows like Numbers? Get a clue.