Mr. Pressius appeared in the second and the third books. In The Perilous Journey, he was one of the important people on the Shortcut. Mr. Pressius was showing off his precious diamonds where one was fake and the others were real which was a part of his plan so he could fool people who might've wanted to steal it with the fake. When the boat lurched, the diamonds all fell and the fake and the real diamonds got mixed together. Reynie helped solve which were real or fake by saying that if they were all put in a tub of water, the real would sink to the bottom and the fake would float.
In The Prisoner's Dilemma, he came to Mr. Benedict's house with forged papers declaring that he was Constance Contraire's father. Constance then uses the Whisperer to get her memories back and learns that Mr. Pressius is not her father so Mr. Pressius (who is thought to be working for Mr. Curtain) couldn't take Constance.
The government of Stonetown, desperate for funds, sold the tidal turbines they seized from Ledroptha Curtain to Mr. Pressius. Unofficially, Mr. Pressius was to sell back the energy produced by the turbines to the government at a very modest rode. Mr. Pressius, however, was under Curtain's control, as Mr. Curtain wished to regain use of the turbines to power the Whisperer. Mr. Pressius acted under Mr. Curtain's orders to cut power to the town. After Mr. Curtain's defeat, he and Curtain lost control of the turbines.