What about Rhys's lovely mummy arriving early and catching Gwen and Rhys in a compromising possiton on the couch.

Then Jack and Tosh arrive with a sedated Wevil that they have just caught in the SUV, but while they are telling everyone a story about having to do something at work so they can take the Weevil to the Hub first and come back a bit later, the Weevil wakes up an escapes and somehow ends up in the flat an surprises Rhys's mum in the bathroom.