The CIA team's hunt for Perseus has led them to the KGB headquarters in Moscow, along with the cache of sleeper agent being stored inside a nuclear bunker underground. With only one way in and out of the bunker, Russell Adler decides to call for Dimitri Belikov, their mole in the KGB, to get them inside. Sims is skeptical that Belikov will honor his word, but Adler insists that he will get them through. Adler and "Bell" are sent to undertake the mission, with Belikov watching their movements. Belikov finds that the security measures have been increased, just as a soldier informs him that Gorbachev has requested him for a high-level meeting. Upon arriving at the meeting, Gorbachev states that there is a mole among them, and that they must be found. As a safety precaution, all but General Charkov's bunker access has been revoked. Belikov disables the building's CCTV before making his move to acquire a key: Poison Charkov Stab Charkov Reprogram a key Frame Charkov Ivanov kills Charkov Belikov decides to take Charkov's key by poisoning him with Nova-6. He enters Kravchenko's office and steals a bottle of Nova-6, before requesting a meeting with Charkov's receptionist under the guise of having some tea. The receptionist brings him into Charkov's office, where Charkov is busy talking to someone on a phone as the receptionist pours tea for the two. Belikov pours the Nova-6 into one of the cups, but Charkov takes the non-poisonous tea; fortunately, Belikov is able to swap the two cups as Charkov is distracted. Charkov then states that he already knows that Belikov is the mole and that he wants his card key, but dies from ingesting the poison. Belikov takes the card key and leaves through a side office. While acquiring the key, Belikov can take out Richter. After acquiring the key, Belikov makes his way to the basement and enters the furnace room, where Adler and "Bell" are waiting for him. As they need disguises, Belikov calls for two officers to investigate an open door. The two then ambush and kill the guards, taking their uniforms as a disguise before making their way to the bunker area. Adler and "Bell" then make their way, gear in tow, eventually arriving at the entrance. They try to bypass through a side door, but are caught by a guard, who insists that everyone must go through the checkpoint. Just as it seems that their mission will be compromised, Belikov comes through once again to get them through, where they take the elevator to the bunker. Before the elevator doors close, Zakhaev enters and asks the two who they are and where they are going. Knock out Commander Sobol Commander Utkind/Petrov "Bell" chokeholds Zakhaev before Adler sucker punches him out cold. Regardless of how Zakhaev is dealt with, the two discard their disguises and begin equipping themselves. They engage in a massive fight to get to the vault; halfway through, Adler has "Bell" set up a secondary plan by placing a gas can in the ventilation system if their escape is compromised. Entering the vault, "Bell" quickly copies a list of the sleeper agents in the United States as the two attempt to escape before reinforcements arrive. As the pair fight their way out of the KGB headquarters, the two run into a group of soldiers with a captive Belikov, having realized that he was the mole. Adler, refusing to let Belikov die, has "Bell" activate the gas to save him. Belikov, grateful for the rescue, informs the two that the Soviets are locking the building down. They take a brief detour to the armory to arm and equip themselves with Heavy Armor and escape in their get-away vehicle with the intelligence in tow.