Expect serious resistance from the police units after arriving at the plaza. All the machines you've destroyed will appear again, along with heavily armed opponents equipped with Volley Guns.
You will now have a chance to finish an optional mission involving the Vox code in the watchmaker's store. Return to that shop and follow the instruction by using the clock found on the wall. You'll be rewarded with Infusion #14, Voxophone #42 and several less important items. Once you're done exploring the plaza return to Chen Lin's workshop.