Jessica was a girl at the community centre who was organising a charity run after her mother's death from cancer. Nathan initially sees her changing after a run in the community centre, but begins to suspect her of more violent behaviour when he is subsequently murdered in the toilet (Although the lights being turned off prevents him seeing the guilty party). When Jessica begins to express an interest in Simon, Nathan grows increasingly concerned about Simon, particularly after he sees Jessica talking with someone else and the boy subsequently falls dead with a slit throat.
During Nathan and Alisha's attempt to 'prove' her role in the deaths, the body of the previously murdered victim vanishes while Jessica is having a drink with Simon, causing Simon to conclude that they are lying. When the Misfits are attending a fancy dress party, it is revealed that Jessica's father, Dave , is the one committing the murders to 'protect' his daughter; he attempts to kill Simon, but ends up killing someone wearing the same costume as Simon by mistake. While Jessica and Simon sneak off to have sex in a toilet- Jessica revealing that she is actually a virgin, most likely due to her father's over-protective nature-, they are caught by her father in the aftermath, who attempts to kill Simon before Alisha stops him by hitting him in the head with a fire extinguisher. (S02E05)
Jessica then ends the relationship because of her recently jailed father. (Dinner Date)