No one performs on the circus trapeze like 16-year-old Rémy Brunel. But Rémy also leads another life, prowling through the backstreets of Victorian London as a jewel thief. When she is forced to steal one of the world’s most valuable diamonds, she uncovers a world of treachery and fiendish plots. Meanwhile, young detective Thaddeus Rec is determined to find the jewel and clear his name. Will Thaddeus manage to rescue the jewel? Or is it really Rémy that he needs to save?

Trapeze-artist Rémy has left the circus and her life as a thief, but she doubts that detective Thaddeus Rec will ever truly trust her. Feeling torn between her new life and her old, Rémy decides to return to France and her old circus with Yannick, an old friend who unexpectedly appears. Meanwhile, Thaddeus is sure that Yannick is up to no good. He's determined to find them and win Rémy back, even if he must risk a journey by airship to do so.

Remy and the Ruby Airship's crew have traveled deep into the Indian jungle to learn the truth behind the mysterious Sapphire Cutlass. But Remy is torn between helping her friends and finding her twin brother. Will her choice put everyone in danger?