Final answer:
Wilson discerns there is another man involved through secretive glances at a paper, conversations pointing to espionage, and out-of-place signals such as a man waving a coat in what seems like a nonsensical context.
Step-by-step explanation:
Wilson gathers clues suggesting the existence of another man through various instances that hint at secretive behaviors and unexpected observations. From catching people looking at the paper when they think they're unobserved, to overhearing conversations about being spied upon, these events cumulatively imbue Wilson with a sense of suspicion.
Added to these are sightings of signals and signs that are out of place, like a man waving a coat when supposedly there's no need for a signal, or a figure trying to remain hidden while keeping watch, further suggesting the presence of another individual with unspoken intentions or secretive actions.
These snippets of information collectively paint a picture that leads Wilson to deduce that there’s another man involved - hidden actions, private malice, and disparate pieces of evidence that something is not as it seems.