During this they also discover the reason they were ordered to do so, was mainly because they wanted to see why Spider-man had been able to become a hybrid spider/human cross, when experiments with others human/animal failed. When these experiments escape and start killing people, a cure is found that will kill the hybrids.
Spider-man does the heroic thing and releases the cure across the city, knowing that it will kill him as well. As he is dying he makes it back to the tower to say goodbye to the team.
I think I found it one time on Archiveofourown, but search has failed me.