Dual Purpose is a mission in Marvel's Spider-Man. Prior to the explosions in "And the Award Goes to...", Peter Parker was sure he saw Martin Li at the scene with the Inner Demons. Though he tries to convince Yuriko Watanabe of this, she demands he find evidence before she can do anything.
Mary Jane Watson calls Peter Parker with a tip about Li and a recycling business he bought a controlling interest in. She also reveals what the arrested Inner Demons have said about Li – that he brings out the "negative" side of people so they do things they normally would not do.
Upon entering the building, Spider-Man finds a map that appears to target all of the campaign offices of Norman Osborn. Further evidence includes gadgets, explosives from the construction sites of Wilson Fisk and his weapons, and blueprints for truck bombs. He finds the address to their next hideout, and and then proceeds to that area.
After clearing the guards at Consolidated Shipping, Spider-Man finds another map to the Demon Warehouses throughout the city, as well as additional evidence. After defeating more Demons outside, Sable International arrives. Spider-Man does not know who they are, and Silver Sable arrives herself via helicopter. They manage to capture Spider-Man using trap gadgets, and it is only through Yuriko Watanabe's timely arrival that he is ordered free. Yuri lets him know that Osborn has hired Sable for protection.
Upon arriving at the waypoint, several Inner Demons guards are found at the area, and must be defeated with either open fighting, stealth-webbing from above, or a mix. Follow the next waypoint to the door then find the junction box to the left and use the Electric Web to short it out. More circuit junctions should be tripped in the same way, and then access to the building is gained. After a crawl through one of the vents, Spider-Man arrives in the room where the evidence is located. After interacting with the items in the room, an address is found to the next area, Consolidated Shipping.
At Consolidated Shipping, it is obvious it is heavily guarded, with plenty of snipers. At this point the Trip Mine gadget is unlocked for use, as this part of the mission relies on stealth. The Mine only has a few charges, so players need to be careful where and when they use them. The snipers should also be dealt with as quickly and quietly as possible, as alerting one will typically alert them all, and then the fight can get tough.
Upon entering the office, a map reveals the Demon Warehouses throughout the city, which can be cleared out for Base Tokens. Leaving the office will begin a battle with a member of the Inner Demons wielding two "negative" whips. The easiest way to deal with the whip enemy and those like him is to use throwables, avoiding air combat. Webbing them normally does not seem to be very effective, though it works somewhat just after they attack with a whip, and can defeat them after first hitting them with a throwable.
More Demons arrive. Upon defeating them, a cutscene commences, leading to the next mission, "Hidden Agenda".