Line of Duty viewers were convinced DCS Patricia Carmichael dropped a huge clue during last night's episode.
Carmichael, played by Beverley-born Anna Maxwell Martin gave a huge clue by rapping out Morse code during an interview.
The officer was overseeing the interrogation of Acting Detective Superintendent Jo Davidson (played by Kelly Macdonald) following her arrest after the shooting of PC Ryan Pilkington.
She led the explosive interview during Sunday night's latest episode, accompanied by Superintendent Ted Hastings (Adrian Dunbar) and DI Steve Arnott (Martin Compston).
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Fans are convinced the small signal has completely given away her identity as shadowy villain H, the Mirror reports.
During the very tense chat, she was seen rapping her pen on the table four times - and fans think she was actually using Morse Code.
Four taps is Morse Code for H and was previously used in the show by dying copper Dot Cottan as he passed on a cryptic message about dodgy police officers.
One fan wrote: "Whilst interviewing Davidson, Carmichael taps her pen on the table 4 F*****G TIMES!! We all remember Dot's message when dying, 4 Dots .... 4 taps in Morse code? F*****G H!!!"
Another tweeted: "I've come up with a few theories from last night's #LineofDuty."
They added: "One of the biggest takeaways for me was when DCS Carmichael, when interviewing Jo, tapped her pen four times, potentially signalling Morse code.
"Did anyone else pick up on that? I noticed it immediately!"
One more was convinced the code was Carmichael's secret signal to Davidson to shut her up, writing: "#LOD Four dots in morse code means H??? Carmichael tapped her pen 4x in the interview tonight to shut the DI up! Hmmmm???"
Actress was questioned about the Morse code theory during an appearance on This Morning today, and she burst out laughing as she denied the pen tapping had any hidden meaning.
She said: "I think I was just bored cos those scenes are really long. I was like what am I saying next?"
However, it's done little to stem with speculation around Carmichael, with some fans convinced she was also behind the botched raid on the home of dodgy detective Marcus Thurwell, played briefly by James Nesbitt.
The character was hiding out in Spain but was killed in a police raid on his home before he could get any actual screen time, with some fans convinced he actually faked his own death and walked out dressed as one of the police team.
However, some think Carmichael ordered the raid to frame Thurwell.
One wrote: "Hear me out. Carmichael tapped her pen 4 times in the interview (morse code for H).
"Carmichael also knew Thurwell would be exposed so she had him killed and used a VPN to set her IP address to Spain to frame him as being the Unknown user Jo was taking orders from."
Line of Duty continues on Sunday 2 May at 9pm on BBC One.
