Ten Thousand Skies Above You (Firebird) by Claudia Gray

Marguerite’s parents are famous scientists who not only discover that multiple dimensions co-exist all around us, but invent a small device that allows a person to travel among these dimensions and inhabit our “other dimension” self, one at a time. Needless to say, it’s a world-altering discovery/invention but Marguerite’s father is murdered immediately following the discovery. One of his two trusted lab assistants, Paul, is accused of the murder (we don’t know by what evidence), and Paul skips town. Or rather, he skips their dimension entirely using the newly invented device called the Firebird, hence the series title. Marguerite and the other lab assistant, smarmy Theo, take two more Firebirds and chase after Paul to extract revenge.

In this sequel to A Thousand Pieces of You by New York Times bestselling author Claudia Gray, Marguerite races through various dimensions to save the boy she loves.

Ever since she used the Firebird, her parents’ invention, to cross through to alternate dimensions, Marguerite has caught the attention of enemies who will do anything to force her into helping them dominate the multiverse—even hurt the people she loves. She resists until her boyfriend, Paul, is attacked, and his consciousness is scattered across multiple dimensions.