Callum (Laurie Duncan) grows increasingly suspicious of Ally in next week's episodes, and later becomes determined to expose him as a liar when he discovers that the mysterious Australian is using multiple aliases for reasons unknown.
As seen in pictures released at the weekend, Callum's efforts come to a head when he does some digging and confronts Ally with three women from his past.
Speaking to Soaplife about the storyline, O'Connor commented: "These three women are standing right in front of him and he's got to think of a story fast, but he's a good liar and he doesn't panic. He's always got a good story to back his lies up, so he might get away with it."
Asked who the ladies are, the actor replied: "All will become clear. For now, I'll just say Ally has a very dark and mysterious past. He's not the nice guy everyone loves."
O'Connor also explained that Hollyoaks viewers should not necessarily believe everything that Ally has told the villagers about himself.
He admitted: "Ally hasn't said much really. He's supposedly an army medic who suffers from post-traumatic stress disorder, but that might be a cover-up. We don't really know what's true after Callum's revelations."
Hollyoaks airs weeknights at 6.30pm on Channel 4, with first look screenings at 7pm on E4.