The show newcomer, played by Over The Rainbow star Stephanie Davis, vows to start her time at Hollyoaks High with a bang by coming up with a practical joke for the deputy head.
However, Sinead's younger brother Finn is not so keen on the idea and steps in to stop her planned victim from being left covered in water due to the trap she's set.
Immediately afterwards, there are two twists when the school head teacher falls into the trap instead, ending up unconscious - and it's revealed that deputy head Rob is Sinead and Finn's father…
Hollyoaks airs tonight at 6.30pm on Channel 4.
> Click here to read more about tonight's episode
> Click here to read our recent interview with Stephanie Davis