In Victorian London, Dr. John Watson approaches a gang of troubled teenagers living on the streets, and ropes them into investigating a series of horrific and mysterious crimes, whilst his business partner - the elusive Sherlock Holmes - takes all the credit.
As the crimes begin to take on a supernatural edge, it's up to the Irregulars - alongside their prince-in-disguise ally Leopold to come together to save not only London, but the entire world.
The Irregulars provides examples of:
- Adaptational Attractiveness: Mycroft is portrayed by Jonjo O'Neill, who is a far cry from the large and portly character described in the books.
- Adaptational Jerkass: John Watson, Holmes, Inspector Lestrade and even Ms. Hudson are much nastier people here than in the original Sherlock Holmes canon.
- Adaptational Sexuality: John Watson is gay in this adaptation.
- Adaptational Wimp: Compared to the literary Mycroft, whose observational skills were at least on par with those of Sherlock, the Irregulars version doesn't display any such
- Adults Are Useless: Including and especially Sherlock Holmes himself.
- Affectionate Nickname:
- Billy calls Bea "Bumble" occasionally.
- Bea and Jess' mother, Alice, calls Bea "Bea-Bea" when they meet in the season finale.
- Ascended Extra: The Baker Street Irregulars, whilst well-known, appeared very little in canon.
- Asshole Victim: Episode 4's victims-of-the-week (except arguably Lestrade, although he was a jerkass) were these.
- Baker Street Regular: The Trope Namer gets a show for themselves.
- The Beastmaster: The Villain of the Week of the first episode can control birds.
- Crazy Jealous Guy: Subverted, while Billy is clearly in love with Bea (and she may be with him too) and he is jealous of her growing closeness with Leo, he backs off after he sees Leo make her laugh, even though his feelings are still there.
- Darkest Hour: The end of "Chapter Six: Hieracium Snowdoniense". Leo's identity has been revealed to Bea, who has ended their relationship and prompted him to go back to the castle. Bea also drives a wedge between herself and Jessie by joining the others in encouraging her to go deeper into her nightmares to find answers. Billy has been arrested for killing his abusive former workhouse supervisor in self-defense. Worst of all, Jessie finally meets The Linen Man in person - and he reveals his true, evil intentions.
- Deal with the Devil: In "Chapter Seven: The Ecstasy of Death", Sherlock lets The Linen Man out of a trap he and the others had set and goes with him. The next episode reveals that he helped him in order to get Alice back from beyond the Rift.
- Eye Scream: The homicidal birds in "An Unkindness in London" seem to enjoy going for people's eyes.
- Family of Choice: The Irregulars are this to each other.
- Foreshadowing: In "Ipsissimus" Mycroft Holmes passes off Bea and Jessie as his nieces to explain their presence in the house. Come "Students of the Unhallowed Arts" it is revealed that they actually are his nieces. Jessie is Sherlock's daughter and Bea was for all intents and purposes Sherlock's stepdaughter.
- Five-Man Band
- The Leader: Bea. The leader of the group
- The Lancer: Jessie. Has supernatural powers which make the whole plot possible
- The Smart Guy: Leo. His better education and social connections mean he knows things the others don't
- The Big Guy: Billy. The tallest and the most likely to solve a problem by hitting someone
- The Heart: Spike. Thinks of himself as a charmer. Works hard to bring the group back together when they fall apart.
- Historical Domain Character:
- Prince Leopold
and his older sister Princess Louise. - The Hermetic Order of the Golden Dawn also turn up.
- Prince Leopold
- Kid Hero: The titular Irregulars are all teenagers, as is their ally Prince Leopold.
- King Incognito: Leopold pretends to be merely "Leo", just a posh boy who most definitely is not a prince.
- Magical Negro: The Linen Man rescues Jessica from the Plague Doctor with a magical cloud of butterflies, explains what she is and why she is seeing things, and advises her on how to figure out what is going on. But he can't solve her problems directly as Jessica is in London and he is in Louisiana. Subverted when he shows up in London for real and starts killing people.
- Manly Man and Sensitive Guy: Billy and Spike
- Mythology Gag: Sherlock namedrops "the case of Jefferson Hope" when explaining how he met Dr. Watson.
- No Historical Figures Were Harmed: Most of the members of Hermetic Order of the Golden Dawn shown in "Ipsissimus" are Expies of members of the historical group of the same name:
- Alan Crawley for Aleister Crowley
- R.P. Breakwater for either Bram Stoker or Arthur Machen
- Dion Cross for Dion Fortune
- Gustav Felkin for Robert Felkin and Gustav Meyrink
- Patricia Colman Jones for Patricia Colman Smith
- Richard Wynn for William Wynn Westcott
- Oh, Crap!: Billy is completely undaunted when he is paired to fight a boxer much bigger than he is, but when Bea appears, furious at him for participating in a dangerous fighting ring, her face alone causes him to have this reaction.
- Parental Abandonment: All of the Irregulars are street kids with missing parents, either by death or abandonment. Even Leo has a distant relationship with his mother as she is kept occupied by her role as the Queen.
- Race Lift: The colourblind casting gives us a black John Watson.
- Tomboy and Girly Girl: Bea and Jessie respectively.
- The Tooth Hurts: The mystery in "The Ghosts of 221B" revolves around people having all of their teeth stolen.
- Tooth Fairy: The Monster of the Week in "The Ghosts of 221B" seems to be one of these.
