Hidden Agenda is the twenty-second main mission in Marvel's Spider-Man. Yuriko Watanabe contacts Spider-Man to let him know they located the evidence from the "Dual Purpose" mission, but that none of it points back to Martin Li. Spider-Man decides to return to the F.E.A.S.T. shelter to see if he can find any information.
While there as Peter Parker, he suggests to Aunt May that Miles Morales might be a good person to hire. He then decides to search Li's office, entering through the ventilation duct as the door was locked. There, Peter finds a note written to May in which he expressed genuine belief in F.E.A.S.T.'s mission, but also warned her that he would be written about as a criminal. He also finds an entry in Li's journal exxplaining that the arrest of Wilson Fisk allowed the Inner Demons to capture his weapons and use them against Norman Osborn, but lamenting that this would mean giving up F.E.A.S.T., saying that while part of him wishes to turn back, the "demon is hungry" and he is not strong enough to hold it back.
Peter then finds a secret room behind Li's office. Here, he sees found Inner Demon weapons and deduces that Li was giving his powers to the other Demons, a board with news stories about Norman Osborn. He also finds a recording by Li in which he notices his power growing, lamenting that father would say he has lost balance, but that "the only way to fight a monster is to become one". Lastly, he sees the file folder on Devil's Breath that Mary Jane Watson had found at the auction house earlier, and unfortunately trips a booby trap that turns the room into a sparking "burn room".
After escaping the trap, Peter left and bumped into Li on the way out. Their very short conversation is interrupted by Aunt May. Li does not seem concerned that he found Peter exiting the room, only announcing to Peter and May that he will be leaving town yet again. Peter follows him outside, watching him get in his car, but then is attacked by homeless people who are apparently under sway of Li's "negative" power. Only when they are knocked unconscious do they return to normal.
With the evidence of the Devil's Breath file in hand, Peter calls Watanabe to inform her what he found in the center in F.E.A.S.T. center in Chinatown, as well as the possible attack by Martin Li using Devil's Breath, apparently a potential bio-weapon created by Oscorp. He also fills in Mary Jane Watson, agreeing to meet her for dinner. While Peter ponders what to cook, Otto Octavius calls and urges him to postpone dinner plans and meet him in the lab.
The player controls Peter Parker throughout the mission. After entering the F.E.A.S.T. shelter, following a cutscene, the objective is to investigate Martin Li's office, which is locked, forcing players to use the ventilation ducts as a point of entry. Once inside, many objects are available for investigation. The key found in Li's journal in a drawer and the picture of Li and May are required to progress.
Using the key to reach behind the picture of Li and his wife and completing a simple puzzle lock behind it (making a Taoism symbol in) opens a room beyond. There are many items to inspect, but the important one for progression is the file folder on the desk. Taking it and leaving trips the next section. Here, players need to hang upside down from the ceiling and use their Electric Web to short out the circuit breakers all over the room to disable the trap.
After the room is safe, players must drop to a room in the grating below and then escape by pushing an object in front of a door. Cutscenes then complete the mission, and afew a few phone calls with Yuri, Mary Jane, and then Otto Octavius, the next mission, "A Fresh Start", begins.