Gary Sinise and David Caruso Gary Sinise and David Caruso

Anyone who wants a free — albeit rather blood-soaked — trip from the Sunshine State to gritty New York City need only tune in to CBS' massive CSI: Miami-CSI: NY crossover, beginning tonight at 10 pm and reaching a shocking climax on Wednesday at 10 pm/ET. In the sprawling saga, a mass murderer in transport to Florida becomes a man on the loose, offing a lot of people who get in his way and ultimately leading Miami's Det. Horatio Caine (David Caruso) to the Big Apple, where he and NY counterpart Mac Taylor (Gary Sinise) pull out all the stops to ferret out the fugitive. The case is so complex and the killer (played by 24 good-guy James Badge Dale, no less) so chilling that of course it demanded two CSIs.

The genesis of the endeavor came with the previous crossover, when the Miami cops appeared on NY to help launch the second CSI spin-off. "We were shooting a scene in which David comes out of a New York apartment building with Gary, and the way those two talked, they just had this give-and-take that was so cool," says Miami executive producer Anne Donahue. "So what happened for me was that I wanted to be with them again. From that moment on, standing there in NYC, I said, 'We have to do a crossover.'"

But not right away. No, CSI: NY needed to establish itself first for it all to work. "When we were launching NY," says CSI creator and NY executive producer  Anthony Zuiker, "we were busy trying to build an audience, competing against Law & Order and trying to get our sea legs. But with the total change in NY this year — we've had a complete visual makeover — and because it's going in the proper direction, this is really what the doctor ordered. It really treats our audience and gives NY that extra boost. It couldn't have come at a better time."

A better time, that is, unless you're one of the many, many bodies that fall in the crossover killer's wake. "I believe it's six bodies on Miami and seven on NY," says Zuiker. "But it's organic in the way the story came about. With dead bodies, there are stakes, and with this crossover the stakes are so high. That's what makes it special, and not gratuitous."

Still, we can only imagine the number of toe tags needed should CBS ever brave the ultimate triple-CSI crossover-and-over-and-over, using all three shows. "You never know," Zuiker smiles at our suggestion. "The beauty of this franchise is that it's very interchangeable in terms of how the combinations will work. But if you do too many of these a year, you run the risk of killing the writers!"

Not to mention the actors. "The week that we did the crossover, David Caruso — as well as Gary Sinise — was doing three episodes at once on different days," shares Donahue. "And David's son was born that week. He welcomed a beautiful baby boy while we were shooting. So our hats are off to him and his family for that."