We first heard of “H” in Line of Duty after corrupt copper Matthew ‘Dot’ Cottan’s dying declaration in season three.
When DI Kate Fleming started spelling out the alphabet, that letter was all he managed to give Kate before he died.
At first it was assumed this was the first letter of a surname, like Hastings, but then it came to light that H is actually a codename.
In season five, a re-examination of Dot’s dying declaration showed that by using his left hand to tap out “dot dot dot dot” (‘H’) in Morse Code, Dot was apparently trying to tell Kate that there were four “Dots” – i.e. four “Caddies”.
We now know that three of these were Dot Cottan, Gill Biggeloe, and Derek Hilton.
But who is the fourth man, or woman?
In last night’s episode, DCI Jo Davidson was taken in for questioning about her involvement with organised crime following the death of Ryan Pilkington.
DCSI Patricia Carmichael, who, it was announced, is taking over Superintendent Ted Hastings as head of AC-12, revealed to Davidson aspects of her disturbing family history she hadn’t heard before.
It was SI Ted Hastings that was pushing for an answer as to Davidson’s knowledge of who H might be, asking if she had ever seen Marcus Thurwell, the SIO in the Christopher Lawrence case.
At this point, all fingers were pointing to Thurwell as the fourth man, but it was a more covert clue which viewers are convinced gives the game away.
During the questioning, DCSI Carmichael can be seen tapping her pen four times.
Four dots, as we know, is H in Morse code.
It’s a revelation which has driven fans of the show crazy, with one saying: “How have Steve and Ted not gotten suspicious of her yet?”
Whereas others think the clue might be too obvious, with one user commenting: “I think it’s too obvious to be her. 4 taps in morse code is H. They're playing us surely?”
It follows a string of other clues which point to DCSI Carmichael as H.
One viewer tweeted: "We all know Patricia Carmichael is H. Jimmy Lakewell said 'look beyond the race claim to find H'.
"So take the letters of RACE CLAIM from the letters of CARMICHAEL. What do you get? H. Solved it."
Picking up on the same thing, another fan posted: "Look beyond the “Race Claim” is also spelling Carmichael with H missing."
