Captain White briefs the Avengers, telling them that Doom’s people are going to make an exchange with Hydra’s people. What could they have to trade? Not sure, but the goal is to find out, and sour the exchange if possible without a massive bodycount or giving away SHIELD’s involvement too much.
The secure location for the trade will be the opening of Atlantis, an arcology on the sea floor off the coast of Great Britain. The Avengers will get on a bullet train that goes down under the water, and attend the opening ceremony. Somewhere along that high-security weapons-free chain of events, the unknown agents of Hydra and Doom will trade information.
Mister Fister is to be the weapons and equipment officer for the trip, with all their gear shrunk down with him as he rides in a lipstick case. Benny is Jethro Tanvers, oil baron, and Sister Sunshine is Selina Wyld, a diamond heiress.
They check out the hotel occupants before the train is scheduled to go. In the bar, they identify Lady Viper, one of Hydra’s top agents; she palms Mister Fister’s wallet and gets his identity, putting his wallet back; that could be bad in the future. Lady Viper is Ms. Amoire, attendant to Lady Elva, Duchess of Cornwall. They also identify Lady Ana Selkie, a Symkarian official who might be Doom’s representative.
They pull the fire alarm, clearing people out of the highly-secured hotel, as well as bugging prominent suspects. Eventually they make it to the train station, and get through the security to board. On the train they realize Lady Selkie is also trying to identify the spies who are part of the exchange.
They reach Atlantis and Mr. Weyland gives the opening speech in these international waters. They identify the Grim Reaper here in disguise also, another of Hydra’s deadliest agents. After the speech, Weyland goes to intercept Madame Viper—Weyland is Doom’s agent?!
Mister Fister goes to work, stealing the drive from Viper’s pocket and leaving a flash-bang that makes it look like the drive exploded, like she was betrayed. Meanwhile Benny is identified, and put in custody, and when Wayland goes to talk to him he palms the information off the billionaire.
Sister Sunshine cuts a deal with Lady Selkie, who agrees to pretend Benny is her employee. She pulls him out of custody, and Sister Sunshine pumps the Reaper full of trank darts so he cannot interfere with the escape. Lady Selky has a prepared hack to take over one of the escape pod lifeboats.
As they are escaping, other submarines rise to intercept, but SHIELD is closing in from above; a tense chase results in Mister Fister getting out and swimming, at huge size, with them holding on; they reach the rendezvous spot and SHIELD picks them up.
Later they find that Doom was trading initial plans for some kind of power armor—like the prototype in the SHIELD vault on the Helicarrier!