On a summer evening, while engaged in an aimless conversation that has come round to the topic of hereditary attributes, Doctor Watson learns that Sherlock Holmes, far from being a one-off in terms of his powers of observation and deductive reasoning, in fact has an elder brother whose skills, or so Holmes claims, outstrip even his own. As a consequence of this, Watson becomes acquainted with the Diogenes Club and his friend’s brother, Mycroft.
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