AThe term 'wet' comes from the Russian expression mokroye delo, meaning 'wet job'. It is a spy slang euphemism for murder or assassination and refers to the spilling of blood. KGB and CIA agents who function as assassins may be referred to as 'wet boys' performing 'wet work' as opposed to 'dry work' like intelligence gathering. Why Marvin added 'like peaches' to the term is most likely an allusion to the fact that it is difficult to eat a ripe peach without getting yourself all wet. What he was definitely alluding to is his contention that the helicopter circling over his house held assassins who were looking to kill him.
AHe knew that Library of Congress numbers start with letters, whereas many municipal libraries use the Dewey system, which is generally a decimal number followed by the Cutter number, which generally starts with the first letter of the author's name. Frank recognizes the number on the postcard as being in the Harvard-Yenching cataloging system used for cataloging Asian books. Stuck in the book with that call number is the list of people who were on the Guatemala mission, most of whom are now dead.
AFrank calls CIA agent William Cooper (Karl Urban) and tells him to bring Sarah to him at the Evanston Power Plant in 15 minutes or will kill the Vice President. Cooper arrives alone, but a limo drives up a few minutes later carrying Sarah, Cooper's superior Cynthia Wilkes (Rebecca Pidgeon), Alexander Dunning (Richard Dreyfuss), and several thugs. While Cynthia holds Sarah at gunpoint, Dunning shoots the Vice President, then orders Cooper to cuff Frank and kill both him and Sarah. The plan is to say that Frank shot Stanton, then Cooper shot Frank and Sarah. In return, Cooper will be made head of the CIA. Dunning explains that he is really the mastermind of the assassinations and that he's just using the CIA to carry out the work. Cooper cuffs Frank as ordered but stuffs the key in his hand. When Frank starts walking toward Sarah, Cynthia points her gun at him, but Cooper shoots Cynthia. Frank applies a crushing blow to Dunning's larynx, after which he hugs Sarah as Victoria, Marvin, and Ivan Simonov (Brian Cox) arrive, taking out Dunning's thugs. The five of them depart together, leaving Cooper to handle the Vice President (who is still alive). Later, in the car, Marvin says he has a feeling that something terrible is going to happen, but Frank says that it can't be that bad because, for the first time, no one is following and trying to kill them. Ivan then reminds Frank of a favor he is owed and asks for his help with 'a small nuclear problem' in Moldova. In the final scene, Marvin and Frank are racing through a Moldovan field, Frank pushing a wheelbarrow containing a nuclear warhead and Marvin wearing a dress, and being shot at by the Moldovan army. 'Next time,' Marvin yells, 'your girlfriend can wear the dress!'