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After collecting the evidence to a crime scene involving a murdered ATF agent who was working undercover, Calleigh is run off the road into a canal, corrupting her evidence. Since almost none of the evidence is salvageable, the CSIs must work to uncover new, untouched evidence in order to solve the case. Meanwhile, Calleigh's ex-boyfriend, also an undercover ATF agent, offers interesting, yet conflicting, insight into the investigation.
Calleigh: But it's (the evidence) all compromised.
Horatio: Yes, everything... but you, ma'am.
Delko: (notices Cooper being a little hesitant about taking an oil sample) Problem, Coop?
Dan Cooper: No, no-no problem.
Delko: You don't know where the oil cap is, do you?
Dan Cooper: I'm just more of a four wheel type guy.
Delko: I got ya.
Horatio: I want you to listen to me. I had a brother who worked undercover just like you and he crossed to the dark side and never came back. Jake, he never came back.
Jake Berkeley: Well, that won't happen to me.
Horatio: Let's hope so, son. Let's hope so.