Karen becomes considerably more mature in series 4, at the end of which she marries the recently freed Jamie Maguire (Aaron McCusker), with whom she co-runs the pub. Series 5 sees her becoming increasingly, albeit grudgingly, more integrated with the Maguire family and their somewhat violent way of life. Karen suffers a miscarriage early in season 6 and very soon after, her changing behavior and the loss of their child starts creating a large rift in their marriage. As she and Jamie argue over shared ownership of The Jockey and other problems, Karen finds herself drawn to her sister-in-law, Mandy's (Samantha Siddall), abusive boyfriend Joe Pritchard (Ben Batt), and has sex with him shortly after Jamie moves out. Joe becomes increasingly controlling, threatening to reveal their affair, and makes a failed attempt to buy out Jamie's portion of The Jockey. During this, the Maguires find out Joe has been physically abusing Mandy, and Jamie is almost sent back to prison after brutally beating him. When Jamie moves back in with Karen, she is able to end her affair with Joe by threatening him that if she claims to the Maguires that he's once again been beating Mandy, they will murder him. The last episode of series 6 reveals Karen to be once again pregnant; however she is unsure whether the father is Jamie or Joe, who laughs and tells her "You belong to me now."