DI Kate Fleming upset Line of Duty viewers after appearing to grass on her old AC-12 unit and ridiculing DI Steve Arnott in the process.
Steve had told Kate about the raid at her new boss DCI Joanne Davidson's office just to give her a heads up, but she ended up informing Joanne so that she was able to stop the raid and delay it.
But during the episode, fans were left feeling very nervous for Kate as she noticed the face of a young officer, who happened to be Ryan Pilkington - the youngest member of the organised crime unit (OCG) who managed to infiltrate the police at the end of the last season.
Ryan was first seen in the first season on the Borogrove Estate and was recruited into the OCG by Tommy Hunter. At the beginning, he was seen just as a courier of burner phones.
He returned in his 20s in series five and ended up slitting undercover cop John Corbett's throat, but his identity in the gang was hidden by fellow member Lisa McQueen - allowing him to be accepted for training as a Student Police Officer.
18 months have since passed and Ryan appears to be close to Joanne - but as he appeared in the office, Kate was sure she recognised his face.
But one fan reckons that Kate already knows who he is after spotting his picture and profile on her computer screen.
Sharing grabs, they tweeted: "Kate knows!! #LineOfDuty did anyone else clock this??"
Other fans flocked to comment, with one writing: "What a spot. Thought you'd edited it, but been back and watched it again. Kudos."
While another joked: "You could spot an armed robbery down a side street from a speeding police car."
A third wrote: "No. I totally missed it though I noticed she was looking at him funny. Thanks."
"Think somebody should be working for AC12 we that skillz," another quipped.
*Line of Duty airs Sundays at 9pm on BBC One