Dex went on a date with Mandy Maguire in Series 5 that ended in apparent tragedy. Dex mentioned having a young son named Johnny, he and Mandy bonded over the fact they were both single parents to young children. Mandy was set up with him by Ian and her brother Jamie who told her Dex was a friend of Jamie's. However a little while into their date, Mandy discovered that Dex wasn't a friend of Jamie's at all but Ian and Jamie had set up an online dating profile for her and chosen Dex as the best match.
Mandy returned to The Jockey to angrily confront Karen, as Jamie and Ian had gone on a "boys night out", but as Karen was appologizing Dex appeared and kissed Mandy. The couple stayed at the pub for a few drinks and each took an Ecstasy pill before heading to the flat upstairs to have sex.
Mandy took a break to get herself a glass of water but when she returned she thought Dex had fallen asleep. However after trying and failing to wake him, she checked for a pulse but couldn't find one. Mandy called an ambulance and explained what happened to Karen but then they realized that the last thing he had eat was the pill. Not wanting to face the problems of a drug related death they lied and told the paramedics that they had though an unconscious Frank had swallowed his tongue.
Karen wasn't willing to get involved at first, stating that she and Jamie had worked so hard for the pub. However Mandy pointed out that Jamie wouldn't be willing to let his sister get into trouble and would surely take the blame and end up back in prison. So a trapped Karen decided that they needed to move the body.
They wrapped him up in a rug, moved him in a large wheelie bin and then rolled the body into a ditch. When they returned to the pub they found Ian and Jamie had returned so were forced to reveal what happened to them and enlist their help in the clean up. They burned clothes, dumped the rug, scrubbed every inch of the pub but both Mandy and Karen were struggling under the pressure. Karen was afraid of losing Jamie but Mandy, who was hallucinating and seeing Dex's bloodied head everywhere, soon decided to turn herself in.
Jamie had a plan though and began giving Frank free pints of lager in exchange for him saying he spent the night talking to Dex before leaving with him. Karen meanwhile tried to talk Mandy out of turning herself in, pointing out that there was no need now due to Frank's story but a pale and guilty Mandy had made up her mind.
That is, until Dex strolled into The Jockey, alive and well. He explained that he could only remember part of his date with Mandy and that sometimes when he takes Ecstasy, it can "wipe him out". He wanted to continue to see Mandy and she happily agreed but when Frank spotted him, he claimed that the story he was bribed to learn for the police was true and that Dex owed him £5. Dex handed it over but it turned out that Frank had seen Mandy and Karen moving Dex's body and hinted that Mandy needed to tell him by talking about conscience.
A confused Dex asked what Frank was talking about Mandy was forced to explain, leading to an angry Dex turning down Mandy's apologies and request to start again before storming out.
However the next day Mandy took Katie to the park and found Dex there with his son. Dex was much calmer and the couple agreed to be friends.