Some of the events and many of the characters depicted in the novel have a basis in historical fact: in particular, the mission of Bernard Trench and Vivian Brandon to Germany, the events outside Parliament at the suffragette demonstration known as Black Friday, and the Siege of Sidney Street.
Royal Marines Captain Bernard Trench and Lieutenant Vivian Brandon undertook a spying mission to northern Germany in the summer of 1910, sponsored to the tune of £10 by Mansfield Cumming. The circumstances of their capture in Borkum are related in the novel accurately. The use of flash photography at night did indeed prove their downfall. They were tried and convicted later that year, and spent three years in prison. There is no mention in official records of anyone else in attendance, be it Cumming, Kell, or Wiggins. This is unsurprising, however, as the whole episode was a distinct embarrassment to the British government in general, and the intelligence community in particular.
On the eighteenth of November, 1910, more than 300 suffragettes and suffragists gathered outside Parliament to constitute their own “parliament,” in protest at the decision to ditch the Conciliation Bill granting limited suffrage to women. Eyewitness accounts, as well as photographic evidence, attest to the incredibly rough and violent handling of the protestors by the police. The subsequent police report whitewashes this brutality, as does the report in the Times newspaper the following day. The authorities also did everything they could to suppress the photograph of Ada Wright that appeared in the Daily Mirror. The picture shows her slumped on the pavement, with two policemen looming over her, and rather gives the lie to any notion that the police behaved proportionally.
Contemporary accounts of the events at Sidney Street on the evening of the second and the day of the third of January, 1911, are very similar to the account in the novel. Superintendent Mulvaney organized the preparations for the siege much as described, and the siege turned into a gruesome gunfight that ended in the fire. Huge crowds, Winston Churchill among them, came to watch. The bodies of Fritz Svaars and Joseph Sokolov were found in the wreckage of the house. There is no note in the official records as to the identity of the informant who placed Svaars and Sokolov at 100 Sidney Street. We now know this was Wiggins. Similarly, although the police expected to find Peter the Painter at the same address, his body was never found—indeed, Peter disappeared from any official accounts and was never heard of again. This is another mystery that has now been cleared up.
In his own accounts of Sherlock Holmes’s work, Dr. Watson briefly acknowledges the role of the Irregulars on three occasions. Young Wiggins is cited as the leader of the gang working on two cases—A Study in Scarlet and The Sign of the Four—while in a third case, Wiggins is mistakenly identified as “Simpson.” Dr. Watson’s accounts are notoriously hazy on dates and names, however, and most historical sources are convinced that the Irregulars, and Wiggins in particular, played a far more substantial role in Holmes’s work than Watson credits. This would be in keeping with the mores of the time, where it was rare for lower-class people—and street “Arabs” or urchins in particular—to be given prominence. There is no mention of Tommy, or Big T, in any of Dr. Watson’s accounts. It may also be that after the cases referenced above, Holmes himself wanted Wiggins’s name taken out of any accounts so as to maintain the effectiveness of the child agents.