The episode begins with Peter asking Neal if he has stumbled upon any leads, regarding Ellen’s killer. He shows him an email account though, which isn’t linked to anything else that marshals found at Ellen’s apartment. He has further discovered someone is checking that account regularly, in internet cafes around DC. They both conclude it might be Sam. Peter suggests, Neal get in touch and ask Sam to meet him at a “neutral ground”. Mozzie comes in just then all panicky and tells Neal “someone is trying to kill me”. Both of them calm him down and ask him exactly what happened. He recounts how it all started when June and he paid a visit to market of lost treasures, which is a storage auction.
He and June go through a few storage units but aren’t happy with the contents of any of them. In the end the two come across a unit, the stuff in which they like. Mozzie then makes the winning bid. He then goes through the stuff in the storage unit. He then finds a bunch of two keys and a diary with the initials C.H written on its first page, along with an address. Of the two keys one is modern and the other antique. Turns out, one key opened the door to the apartment of the address mentioned, which Mozzie then enters. Back in the present, Peter tells Mozzie it was inappropriate of him to enter the apartment like that. Mozzie then recounts the rest of the story.
He basically makes himself at home in the apartment and looks around. He then finds himself a secret passage behind a bookcase. He then settles in the apartment, as there is no one living there. Then suddenly he sees a masked man standing in front of him with a gun in hand. The man asks him “where is the flag 723?” Mozzie says he didn’t have a clue what the man was talking about. He is then shown playing along. He pretends to the guy that he knows about the flag. He then manages to disarm the guy and make a run for it, escaping through the secret passage. He then hails a cab to Neal’s apartment. Peter is later informed that Mozzie’s account might just be true. Peter though is still skeptical.
He is also informed that the storage unit is registered to a P.O Box and is owned by someone whose signature is totally unreadable. The apartment as it turns out is owned by a trust, and was originally owned by the 17th century revolutionary Robert Townsend. Nothing though has been found on 723 or C.H. Neal later informs Peter that 723 was the code assigned to Robert who was a spy for George Washington, and was part of a spy ring called the Culper. Turns out, Culper descendants have kept this spy ring alive, is a theory that many believe. Peter though believes it’s a conspiracy theory. Mozzie though immediately buys into this theory and tries to convince Peter of it. Mozzie then from a journal reads numbers which he thinks are codes.
He also tells the two he has broken the codes, and it reveals that Washington gave a flag to the Culpers. The three conclude the flag would be worth a fortune today. Mozzie further elaborates, 723 is talking to 355 about the flag, in code. 355 is Culper’s female spy. As it turns out, the lady Culper might have some idea as to the location of the flag. Mozzie suggests they could communicate with her through “strategically placed messages in newspapers”. The messages are then placed, and the three proceed to the location indicated in the messages, and wait for the female spy descendant. Peter and Neal from a distance later see a woman walk up to Mozzie, who is sitting on a park bench. The two meanwhile introduce themselves in code and begin chatting.
Neal from their conversation finds out that the storage unit used to be an infirmary. He messages Mozzie about it, who then pretends in front of the woman named Tempest that, he knows about the infirmary and its present location. She on hearing this trusts him and hands him a bundle of letters, which she says has been in her family for generations. A man is then seen following Mozzie. Turns out, it’s a guy who has written a book on Culper spies. The man removes a gun, but is intercepted by Peter before he can do anything. Later at the office the guy tells Peter, he was there because he wanted to interview a few Culper spies. He admits that he is looking for the flag, but adds that so are many other people. Peter eventually lets the guy go as he has nothing on him.
Mozzie in a letter given to him by Tempest, finds a ‘sympathetic stain’ which was an invisible ink used by Washington to convey secret messages. The message reads “the secret is in your eyes”. Diana meanwhile finds out that 723 was possibly a guy named Nathan Woodhull, who was a professor. Peter finds out that Nathan was murdered a few months ago by a guy named Cabbot Hawkins, and whose initials read as C.H. Peter later tells Mozzie and Neal he has found out, it’s actually Cabbot, who is agent 723. Nathan as is turns out was agent 722. Cabbot, Peter informs, has been sent to an insane asylum. He also reveals that, he talked to Cabbot, pretending to be 711, which would him the descendent of Washington.
Cabbot claims Nathan was already dead when he arrived, and that he was there to only get Nathan’s documents. Cabbot also claimed to Peter that he had on his own tracked down the descendents of the flag. Mozzie on hearing this is disappointed, as he concludes that there isn’t really a flag. Peter later tells his team that he has arrived at the conclusion; Cabbot was telling the truth about not having murdered Nathan. Stringer, the guy who wrote the book on the Culpers, was in touch with Nathan by email as it turns out and had even accused him of trying to find the flag on his own.
Peter tells his team, Stringer feels the flag is a way for him to win back his lost respect. They all then conclude that Stringer killed Nathan and then went after agent 723. He concluded that Mozzie was 723, as he was in the apartment. Peter though, doesn’t know how he can prove this theory of his. Neal tells Peter they should get Stringer to confess, and they can do this by convincing Stringer that Culpers still exist. Later Stringer is drawn out to the apartment, by a code sent out by Mozzie. In the apartment Mozzie tells Stringer “the boss wants a meeting”. Neal pretends to be the boss. Neal is introduced as 711 by Mozzie, and Stringer immediately latches on to its relevance. Later during their conversation Stringer admits to killing Nathan, and also tells Neal he has the coordinates for the flag.
Neal also gets Stringer to admit, how Nathan suffered while he was being murdered, all the while pretending that he is thankful to Stringer for murdering Nathan as he was a traitor. Then just as Stringer is about to be arrested, Mozzie comes out through the secret passage and helps Stringer escape. Neal tells Peter, Mozzie is trying to get the coordinates, as Stringer would never give them up if he is arrested. Neal then tells Peter, Mozzie and Stringer have probably gone to the storage unit. Meanwhile Mozzie and Stringer find agent 355, standing inside the storage unit. She explains that, she had to see if the infirmary was real, when she got to know about it. Peter and Neal later arrive at the unit, but are late.
They then conclude that Stringer has given Mozzie the coordinates and from the storage unit they have found out the exact place where the flag is, and have left for the location. Then, with the help of a clue left behind by Mozzie, the two, figure out where Mozzie and gang have gone. Turns out, they are at a monument built for revolutionary soldiers. At the monument they find a buried box, but it’s empty. Agent 355 meanwhile manages to disarm Stringer. Mozzie and she then make a run for it. Peter and Neal arrive at the scene just then and arrest Stringer. Tempest later disappears.
She is then seen walking into a basement, with a few people sitting around a table. She walks to the head of the table, removes the flag from her purse and lays it on the table in front of her. Neal and Peter in the meanwhile are a bit baffled as to whether, Culper spies really exist. The episode ends at this point.