Located in the extra-dimensional fourth cloud, in the sky above Metropolis, rests a upside down version of Metropolis - dubbed "Untropolis".
Untropolis spontaneously formed nearly five years ago - which Father Time, of S.H.A.D.E., points out happened around the same time as the Time-Sniper incident (which is classified).
S.H.A.D.E. has a field office in Untropolis, where Frankenstein and his group the creature commandos were sent to, to try and uncover a mole in their organization.
The only way to enter Untropolis is to use Cloud-Packs, which are one-time use for entrance and exiting the cloud. Without the cloud-packs, and the nether-field is creates, you would be vaporized instantly - upon contact with the cloud-dimensional membrane.
Everything in Untropolis is upside down. From the buildings, to the people in the society; an example being that the impoverished live in penthouse suites.
Finding their target among the Untropolis populous is no easy task for Frankenstein and his team. Scarab Agents are brought in by their target, Crowly, to evade capture.