Prototype Blueprints
Piero's "Prototype" blueprints are found in a trashcan by the radiator in Admiral Havelock's vacated quarters on the second floor of The Hound Pits Pub. The blueprints are necessary to allow Piero to complete the Arc Pylon he and Anton Sokolov have perfected. It is located on the roof of his workshop.
Once the Arc Pylon is ready, Piero will ask how Corvo would like it to function: by stunning their enemies or killing them outright.
Once that choice is made, the pylon will still require a whale oil tank for power. An empty tank can be found on the second floor of the workshop and filled at the filling station beside it. The tank must then be brought to the roof and placed in the empty receptacle after using the nearby lever to open the hatches.
The pylon immediately powers up and stuns everyone, including Corvo, though he is only stunned momentarily.