This is the investigation part of case that follows the deduction Who May Know What Happened to the Boy? if the player decides that the Trolls are responsible. This will prompt the line "Find out more about Trolls" in player's questlog. This part of case occurs at the Streets of Twisted & Perverted.
The most likely way for a player to continue this trace is to talk to Mr. Unicorn. This should easily lead to a information about the Trolls' disappearance.
To continue, the player will have to run the exploit on the old Aggregate found in the north-western part of the level (called simply "Generator"). This can be done by using Mr. Unicorn's Two of Clubs card or by solving The Tick's Riddle. The later can be done by examining the Trolls' Campsite and the following the clues found in the player's Codex.
Either way, the player will summon Herman Tick and his fellow Trolls back to their campsite.