Eighty House

Andrew Manson is back in New York City, working on an invention that might ease traffic in the city: a steam-powered omnibus. He's visited by his college friend John Simmons and John's sister Josephine. John's working for the United States Navy on a project, and wants to talk to Andrew about his research. The day after John and Josephine arrive, John disappears from the boarding house they're staying at, and the owner insists Josephine was staying alone. How did John leave Eighty House without Josephine hearing him go? Is he safe? Who are the men following Andrew and Josephine around New York City while they search for her missing brother?