On Monday morning, Calleigh walked into Horatio's lab with a file in her hand. As Horatio wasn't in there, Calleigh decided to leave the file on top of a small pile of other files and folders. As Calleigh turned around to leave, she was hit over the head with a pipe. Calleigh fell to the floor, unconscious.
When Calleigh woke up an hour later, she immediately recognized her kidnapper. It was Rob Cooper, a former technician at the crime lab. He had been fired two months earlier and sent to prison for a month for stealing a dead CSI's credit card. Calleigh had been responsible for the imprisonment and now it seemed that Cooper wanted revenge on Calleigh. She looked around and saw that she was in a basement, tied up at the wrists and ankles.
"You're awake I see Calleigh. That's good because now the fun can really start," said Cooper in a falsely sweet tone.
"Let me go Cooper," replied Calleigh in as calm a tone as she could manage.
"Why should I? Because of you, I spent a month in prison."
"It was your fault that you went to prison. You shouldn't have stolen Speed's credit card."
"Shut-up Calleigh. I don't want to hurt you but I will if you keep going. Horatio should be on his way to get you by now."
"What do you want with me?"
"Nothing, I got over the grudge I had against you a while ago. I want to kill Horatio."
Suddenly, Cooper picked up a rusty screwdriver and drove it into Calleigh's shoulder. This made Calleigh scream in pain and Cooper angrier. He picked up another rusty screwdriver and shoved into Calleigh's leg, making her scream again.
Half an hour later, Cooper had stuck another screwdriver, two knives and a pair of scissors into Calleigh's arm, stomach and leg. He had also used the scissors to slice her breasts open. By now, Calleigh had fallen unconscious.
Summary: Calleigh is kidnapped and tortured as a way of getting at Horatio.