Riley returns to the village next week after Jacqui McQueen (Claire Cooper) makes contact with him and reveals how much his ex-fiancée Mercedes (Jennifer Metcalfe) has been struggling in his absence.
Norbury told TV Times that Riley is sceptical when Mercedes later asks him for another chance, but decides to stay in the area for longer than planned due to Mitzeee (Rachel Shenton).
"[Mercedes is] trying to prove that she can be the perfect girl, but too much has gone on for Riley to buy into that," Norbury explained. "He wants to tie up some loose ends in Hollyoaks, then head off."
He added: "Riley prolongs his stay because of his closeness to Mitzeee. There's a bit of unfinished business there."
Norbury also revealed that Jacqui is equally suspicious of Mercedes's intentions when the feisty McQueen claims to want a happy family life.
"Jacqui is worried that Mercedes just wants Riley, rather than the baby," he said.
Hollyoaks airs weeknights at 6.30pm on Channel 4 with a first look screening at 7pm on E4.
> Hollyoaks' Mercedes shouldn't change, says Jennifer Metcalfe
> Hollyoaks' Rob Norbury reveals Riley Costello return plot
> Hollyoaks' Claire Cooper: 'The McQueens reach breaking point'
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