Summer, year 98 of the Revolutionary calendar, year 1887 of the Imperial calendar. Two young men met in a corner of London. One is Conan Watson, a college student who dreams of becoming a doctor and has just left the countryside for the first time in several years. The other is Arthur Holmes, an eccentric young man who calls himself an inventor and is driven by his own curiosity. The two ended up living together due to a twist of fate or some other occurrence. After a certain incident unfolds in London, he gets caught up in a number of mysterious incidents. Conan witnesses the inferences drawn from Arthur's genius observational eye.