Mercury Williams

"'Promise me one thing? Never forget me. I know your playboy traits, but please - don't leave me.'"Mercury Elsa Williams † was the Swedish-English girlfriend of Liam Stanton and sister of Cassiopeia Williams. She was an RAF fighter pilot who was killed by the Supprimé, courtesy of Danielle Warner, by being shot and thrown into the River Thames.

History
When Mercury was 17, she participated in a Miss Sweden contest and came first. The next three years were filled with her doing more pageants, magazine shoots and some acting gigs. When she was 20, she was deemed "too fat" and retired from the industry. She began working as an RAF fighter pilot, a lifelong ambition she had. She left Sweden, falling out with her family (all except Cassiopeia) and came to London.

Bombing Portugal
She is roped into bombing Portugal with the RAF base in London. In Episode 1.5, she goes on a scouting trip with Liam and afterwards the two spend a night in London together. In 1.8, she leaves the country to visit her estranged family, mends her family bonds, but comes home to find Josephine in her bed with Liam. She accuses Josephine of adultery and Liam of rape. She later forgives both of them.

Miscarriage
In 1.10, it's confirmed Mercury is expecting a baby with Liam. Liam, who is excited but initially against it, says it'll bring them closer together and the two toss around marriage. However, in 2.3, Mercury suffers a miscariage for no apparent reason. This causes Liam to break up with her. Throughout this, Madeleine Stanton acts as a motherly figure, even though she's two years younger.

Death
In 2.5, she's captured by the Supprimé, AKA Danielle, and is questioned as to why she's helping drop the bomb over Portugal. Mercury refuses to cooperate so Danielle shoots her and then her members throw her into the River Thames. Liam mourns for the majority of Series 2 and 3, before meeting her sister in Series 4.

Cassiopeia Williams
Cassie meets with Liam to discuss Mercury's death. Cassie tells him that he should get on with his life, it's what "Mer would've wanted". Cassie tells him not to feel guilty, it was Danielle's fault not his. No one is to blame. Cassie only wants to see her possible ex-brother-in-law happy and right now she's not seeing that.

Alternate Reality
In 7.8, an alternate reality episode, Mercury is still alive as Danielle never turned bad. At the beginning, it seems as though Liam and Mercury are living strong. They are childless, however agree they’re happy. Although they seem perfect, cracks begin to show when Liam shows that he’s still a reckless playboy and this enrages Mercury. Mercury ends up getting in a fight with her husband and accidentally dislocates his shoulder and rewards him with a concussion. This causes Liam to go to the hospital where he meets Jessie Kaletha and Clary Fletcher.