TV's female crimefighters carry a badge, a gun and a tough-as-nails attitude. But there's one tool they're rarely provided with: gal pals.

Sgt. Lucy Bates, assigned to "Hill Street Blues," drank and played poker exclusively with the boys. For all her Southern charm, Deputy Chief Brenda Johnson of "The Closer" can't seem to attract a single girlfriend. Mary Shannon of "In Plain Sight" acts like it's against the law to be even civil to other women.

Until last year, you had to go back to "Charlie's Angels" and "Cagney & Lacey" for a popular drama in which women had each other's back, both on and off the job.

Then came TNT's "Rizzoli & Isles," a formulaic cable series that mixed witty banter with gruesome crimes, neatly wrapped up by the end of the hour.

It didn't appear to be anything more than a so-so dessert to follow "The Closer."

But something extraordinary happened. "Rizzoli" quietly became cable's most watched drama, a title it may well retain as it returns Monday for its second season.

The show's success has much to do with the creators' decision to team a police detective with a coroner without bothering to make one of them a man.

"When I was in 'Law & Order,' Manhattan was kind of the third character," said Angie Harmon, who plays Jane Rizzoli. "In this show, the third character is their relationship."

Martha Lauzen, executive director of the Center for the Study of Women in Television and Film, said creative teams are hesitant to put two women in lead roles on a cop show because they feel the need to feminize the female characters.

"One way to accomplish this is to surround the female lead with one or more male characters who may end up being a love interest or, at the very least, provide opportunities for sexual tension," said Lauzen, who is based at San Diego State University. "In addition, creative teams may be concerned that featuring two female leads as friends, who are already in male-identified professions, may arouse suspicions about the women's sexuality."

The bond between Rizzoli and Isles has its challenges.

Rizzoli, a Boston-bred tomboy who grew up in a family of cops, operates from the gut, a trait that often gets her into trouble both with criminals and with the administration. Maura Isles, raised by a privileged family, is girlier and brainier, a shoo-in to be a "Jeopardy!" champ.

In the end, the two have more similarities than differences, not the least of which is a sense of justice -- and the inability to maintain a love life.

"Even though they are completely different, they still respect each other and like each other," said Sasha Alexander, a regular on "NCIS" before landing the role of Isles. "They also make each other laugh, even though Maura can drive Jane nutty with all her talking."

Both women acknowledge "Cagney & Lacey" as an influence, but they're too young to have been die-hard fans. Still, you can't help but see how the two shows echo each other.

"I remember standing in the living room as a kid and seeing these tough women, and that really resonated with me," Harmon said. "It's come full circle, because I tend to be cast as tough women. That's OK. I'm glad to have a job."

Alexander said the concept wouldn't have worked this time around if she and her co-star didn't have instant chemistry during the casting process.

"Women viewers are very smart and they can smell it when two actresses wouldn't be friends in real life," she said. "You can work at chemistry, but there's something extra that has to happen that's indescribable."

Their tolerance for each other's company was tested in an early episode this season in which the pair try to enjoy a day at a spa, specifically a soak in adjoining clay baths.

The scene, shot in Malibu, forced the actresses to spend five hours in the muck.

"It looked really fun, but it wasn't," Alexander said. "We had neckaches, we were cold and Angie even fell asleep. We couldn't even get out to go to the bathroom and had to drink through sippie straws."

Let's see Cagney and Lacey put up with that ordeal.

njustin@startribune.com 612-673-7431 Follow Justin on Twitter: @nealjustin