Countess Musgrove, whose birth name is Genevieve Decoux, is an eccentric noblewoman capable of considerable subterfuge. As a secret agent for Americans, she is a skilled liar. The Countess is a woman in her forties, with fair skin, mahogany hair and a heart-shaped face. Her clothing is lush and sophisticated, as befits the aristocracy. She seems to be the only American who does not harm Delaney or covet his plans, and unlike her compatriots she has confidence in Delaney and sees him as a generous person deviating from the plans of the Americans to defend Delaney against them.
Countess Musgrove is an aristocrat who comes from New Orleans, determined to have a part in the power struggles between America and the British Empire.
A Game of Shadows
Countess Musgrove held a soiree to which she invited all the London society, including the Geary spouses and James Delaney, who invited Lorna Bow as his plus one. The Countess, once left alone with James during a game, was revealed as Carlsbad by James and the two discussed the terms of their agreement about the trade. 
During a tasteless meal with her husband, the Countess received a visit from James Delaney. The two took a stroll in her garden and confirmed the points of their alliance. The Countess tried in vain to obtain information about Nootka Sound, revealing at the same time that she was just an informant with no decision-making powers within the network of spies. 
Alarmed by the recent arrest of James Delaney by the Crown, the Countess hastily burned some incriminating documents of her involvement with the dense network of American spies. 
While the Countess was playing cards with some ladies-in-waiting in the parlour of her manor, she was visited by Lorna Bow, who passed herself off as a cosmetic saleswoman. The two women spoke in private and the Countess felt threatened and withdrew a dagger from her sleeve and placed it at Lorna Bow's throat. The brazenness of the Countess broke down when she was blackmailed by Lorna, who claimed to be ready to ensure that the Countess would be exposed as a spy if Lorna did not arrive home safe and sound. 
- "As hostess, I thought I would dance the outrageous dance with an outrageous guest."
- ― Countess to James Delaney
- James Delaney: "You sent the giant to kill me?"
- Countess Musgrove: "The outcome persuaded us you should be courted instead."
- ― discovering the first card
- James Delaney: "Countess, I know this is business. And I think I know who you are. But know this. I control the timing of this."
- Countess Musgrove: "At all times your life is in our hands."
- James Delaney: "As is your name in mine, Carlsbad."
- ― Conversation on power game
- Season 1
- S1, Ep. 3: Episode 3 (mentioned)
- S1, Ep. 4: Episode 4
- S1, Ep. 5: Episode 5
- S1, Ep. 7: Episode 7
- S1, Ep. 8: Episode 8
- Countess Musgrove is the person behind the fictitious identity known as "Carlsbad", as revealed in the fourth episode.
- She is originally from New Orleans, according to research by James Delaney.
- In "Episode 8", Countess Musgrove is holding a knife with the word "Allah" (in Arabic: الله) engraved on it. Allah is the Arabic word for God in Abrahamic religions.