TVTV NewsCoronation StreetCoronation Street fans think they know what is going on with Sarah Platt and Gary Windass after some suspicious behaviour recently by both of them on the ITV soap10:43, 21 May 2026Updated 10:46, 21 May 2026Sarah Platt and Gary Windass are hiding something on Coronation Street.‌Now, fans are convinced they are either having an affair, or one of them is Theo Silverton's killer. Either way it's not looking good for Gary's suspicious partner Maria.‌Maria is concerned about Gary acting strangely, while Sarah has been quick to cover for him recently. Gary has seemed concerned for Sarah, and it definitely feels like they are both in on something.‌Viewers have speculated that the night Theo was murdered, Sarah and Gary might have been together. Amid questions surrounding Gary's alibi, with Maria lying for him, fans think Gary and Sarah might have slept together and could now be covering this up.READ MORE: Coronation Street fans 'rumble' what Christina is hiding as exit 'sealed'READ MORE: Coronation Street's Ryan exposes Danielle as fans convinced she's Theo's killerThe other theory is that one of them killed Theo and the other is covering up the crime. Taking to social media, one fan posted: "My latest theory is that Sarah saw Gary either leaving flat or on scaffolding and thinks he did it, but he actually just witnessed it.‌"Still reckon it's either Danielle or their son." Another said: "I’ve had this random thought. I think that Gary killed Theo and it sets up an exit storyline for Mikey because he might be leaving… which kind of explains the NTA nomination??"A third fan commented: "Alright, I don’t think Sarah’s behaviour has anything to do with her head injury. She’s hiding something. I still think it’s an affair with Gry but honestly I can’t be sure."A further post read: "He might not have done it… but I think Gary may know who has," as another said: "Maybe she killed Theo with Gary's help." A fan then said: "Sarah acting erratic because she has to hide the fact that she and Gary are having an affair."‌The theories kept on coming with a fan saying: "I know Sarah is worried about Gary, but she was a little too invested it seems there." One added: "Sarah and Gary whispering? Sarah the killer and Gary helped her cover it up?"As for the affair idea, a viewer commented: "I think they slept together on the night of the murder." This was echoed in a post that read: "She was the one actually with Gary that night?"Article continues belowMeanwhile there were more posts linked to the murder theory. A fan said: "She killed Theo…?" Another said: "She killed Theo! There I've said it," while another wrote: "She killed Theo." A final comment read: "I think she saw Gary kill Theo…"Coronation Street airs weeknights at 8:30pm on ITV1 and ITV X. * Follow Mirror Celebs and TV on TikTok , Snapchat , Instagram , Twitter , Facebook , YouTube and Threads .Choose Daily Mirror as a 'Preferred Source' on Google News for quick access to the news you value.‌ITVCoronation StreetSoap operas