Ellie Simm (Esther Hall) is a restaurant chef, who starts dating Tom Quinn at the beginning of Spook's first series.Ellie is a single mother of her daughter Maisie, 8, after being abandoned by the father.
Tom first meets Ellie whilst he is working undercover as Matthew Artcher (a civil servant working in IT) and subsequently forced to date Ellie under this identity, leaving Ellie unaware of her boyfriends real name and that he is an MI5 agent.
Ellie doesn't find out about Tom's real identity until Traitor's Gate, when Tom is forced to take time off work due to being shot in the previous episode. When Ellie sees Tom's bullet wound, she demands the truth from him, feeling disappointed and betrayed when she finds out she has been lied to ,but begins to accept his career and agrees to continue their relationship.
Ellie and her daughter grow closer to Tom, even moving into his house which prompts him to use his MI5 connects to improve the security of the house, turning it into a fortress. This puts Ellie and Maisie into danger when Tom unbeknown to himself bring a bomb, hidden in a Laptop, into the house after a mission in the series finally, The Lesser of Two Evils and Ellie and Maisie accidentally get locked in with the bomb.
Tom, who is locked out of the house, does everything he can to break into the house to stop the bomb but can't as Maisie has inserted a chocolate covered security card into the door lock, jamming it. Tom attempts to guide Ellie through disarming the bomb in the laptop but she is unable to, leaving the team no way of stopping the bomb killing Ellie. the view is lead to believe the bomb has gone off but it turns out it was a different bomb in another area of the country. The bomb in the laptop at Tom's house fails to detonate when its counter hits nought, saving Ellie and her daughter from being killed.
Ellie after discovering the real dangers that come with Tom's line of work asks him to decide to continue their relationship, making her and her daughter his priority and giving them a safe and loving home or his job as an MI5 agent. Tom, not willing to endanger their lives again chooses work over them ending the relationship, and Ellie and Maisie leave.