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It happened before either of them could do anything about it. Being a gentleman, Mac was just walking her to her hotel room after going out for drinks. And while Mac prided himself on his powers of restraint, Catherine Willows was a forced to be reckoned with.
In New York on a case, Catherine was straightforward, methodical, and, much to Mac's appreciation, cooperative. Her main concern was catching their suspect. Let the District Attorney's worry about jurisdiction. Easily able to goad the perp into a confession, Catherine would be heading back to Vegas in the morning, and Mac, feeling the need to be a good host, took her out for a drink.
Catherine was not a fruity-kind-of-drink woman. Her sense of humor was cynical and her laugh was lovely to his ears. Mac thought he was just making a friend, but in the back of his mind, he knew he liked her.
It wasn't obvious to him until they stood in front of her hotel room door. He meant to shake her hand in thanks for helping with the case but his brain must have mixed up hand signals. Mac's thumb brushed a strand of hair behind her ear and traveled down her jawline to her chin. Catherine didn't pull away, in fact she stepped to him, her eyes bright in question.
Just like that, they found themselves devouring each others mouths; Mac's hand in her hair, Catherine pulling on the collar of his suit jacket. There was a taste of whiskey in his mouth and bourbon in hers but they both knew they weren't even close to being drunk enough to blame this on the alcohol.
They pulled away, looking at each other awkwardly. Whatever chance of friendship was shot to hell by the tension between them.
Mac cleared his throat. "Goodnight Catherine."
A hint of a smile crossed Catherine's face as she also bade Mac goodnight. She entered her hotel room, leaving Mac to wonder what exactly just happened.