Christine is the sister of a close friend of Mac's, Stan Whitney, who was killed in the line of duty several years ago. Mac lost contact with Christine for a while, until Jo and Lindsay demonstrated Facebook spoofing by making Mac a Facebook page while they worked a case involving a guy who was spoofing someone else on the site. Mac got a friend request from Christine, and accepted, and they met later to talk.
Christine and Mac spend the morning in the Park. Christine asks Mac how his doctors appointment went. He tells her he's doing great and that he couldn't have done it without her. Mac and Christine cuddle. Christine begins to image their future together, that she can imagine them sitting in the park when they are grey and old. The two begin to share a passionate kiss when Mac's phone begins to ring. Although ruining the moment, Christine tells him to answer it.
In In Vino Veritas, Mac goes to Vegas while Christine is there. He finds that she has been kidnapped and follows the crime lab's investigation of her disappearance. However, he learns that in reality, the woman kidnapped in Las Vegas was actually an imposter, working with a shady employee of Christine's who owed money to a loan shark. Christine herself was being held in New York. In Seth and Apep, Mac and D.B. Russell take one of the suspects in the kidnapping back to New York and rush to find Christine before the others can kill her.