Don't miss a thing by getting the day's biggest stories sent direct to your inbox Line of Duty fans were agog when one eagle-eyed viewer pointed out an interesting detail going back to the very first episode of series six.
Viewers took to Twitter to marvel after the fan saw what they believe could be a link to elusive fourth man known as 'H.' It was a blink and you'd miss it moment in the BBC One drama about corruption in the police force, but it had fans wondering if it could turn out to be a major clue.
In the very first scenes featuring the mysterious DCI Joanne Davidson in her office was a sign that read "Please return all files once your finished with them Thank you!!!!" Fans think this grammatical error might tie in with other errors
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