First we need to make our way to The Block and grab a fuse to fix Hush's relaxing chair and some poison from downstairs. Then grab the subject's disguise from in the bathroom and talk to the doctor to start the experiment. Don't resist Hush's control. After the experiment ends, Hush will go to his relaxing chair and you can poison the ventilation system on the balcony.
Next, we need to make our way through Royce's lab and clear out the break room. Use our camera to send the other three employees on break and grab the screwdriver from Royce's office to sabotage the plug in the break room. Wait for Royce to clear out the break room and then puncture the water cooler to shock her.
Finally, restart and head to the rooftops to grab a sniper and shoot all the drones out of the sky. This will cause Hush and Royce to meet on a balcony and you can take them out with one shoot.