A married guy, Roy Logan's, girlfriend gets kidnapped, and he gets a ransom demand. Catherine gets a call from a mysterious squeaky-by-helium voice, she disappears, and the team have no idea where she is.
Fortunately, Catherine leaves evidence for the CSIs, such as accidentally-on-purpose skidding a vehicle to leave tire marks. When waiting for Mr. Squeaky Voice's next call, she has a drink at a bar, and Roy gives her a finger. He says the kidnapper left it at Amanda, his girlfriend's house, to get him to pay the ransom. Catherine preserves the evidence in a glass of ice, and places it down at Sara's (who coincidentally is eating at the restaurant/bar with Hank) table, barely making eye contact.
In the end the team find out that Amanda was dead before the ransom demand was made, and that Roy Logan was the killer. Mr. Squeaky Voice was a part played by his lawyer. It was all an act.
This episode was very special, what with the whole Catherine-disappearing thing, and the twist at the end. I honestly thought the wife was the killer/kidnapper. "The Finger" also had a really good opening, of Roy Logan withdrawing money from a bank and constantly looking at the clock. Really fantastic episode. Kept me on the edge of the sofa.