A loose sheet of paper folded between the leaves gave the key.
The book showed that Loge had been employed as an expert operator, in the pay of a certain radical organization, to pull off dynamiting jobs in various parts of the country.

This was his account book with the organization.

He had done his work and taken his pay as methodically as a plumber might.

And he had been paid well.

Cleggett guessed that Loge was not particularly interested in the work in its relationship to the revolutionary cause; it was the money to be made in this way, and not any particular sympathy with his employers, which attracted Loge, so Cleggett divined.