Fiona initially appeared heartbroken by her husband's death, and later got into a fight with pop star Vanna Alabama when she learned that she had had an affair with Seamus. But despite her anger, Fiona assured the player and Jack that she would never have been angry enough at Seamus's infidelities to kill him. Ultimately, though, the evidence proved that it was in fact Fiona who killed her husband.
As revealed by Fiona during her interrogation, she and Seamus's son, Damien, had died some time prior to the case's events, with Seamus claiming that he had been killed in a drive-by shooting. But a few months before, Fiona discovered the true cause of her son's death: he had been playing with one of his father's guns and accidentally shot himself. Enraged at Seamus for lying to her and for keeping guns in the house in spite of his promise not to, Fiona killed Seamus at Dubai's rooftop golf course, splashing hot coffee in his face to distract him before stealing his own gun and using it to kill him. After trying to deny everything, Fiona confessed to Seamus's murder, revealing his role in Damien's death and how she had killed Seamus to make up for not being able to protect her son. Fiona was arrested and sentenced to ten years in prison, to which Fiona tearfully proclaimed that no amount of prison time could be as painful as losing her son.
- Fiona Cummings is similar to Gloria Fernandez, a villainess from the first season of Criminal Case; both are women who kill their husbands for indirectly causing the deaths of their children (sons in both cases) and lying to cover up their involvement; in a striking similarity, both women proclaim during their trial that their punishment would pale in comparison to the loss of their child.