Young adult novel about flying

Question

I've been trying to figure out what the name of a book I read is. There are a couple of things I can remember. The book was pretty recent, I think, and the cover was blue, maybe with birds on it.

• There was a boy and girl as the main character, and the girl was being followed at some point.
• There was a scene where people are flying. I think they drank a potion of some sort, and one person had to jump out of the window before being sure they could fly. The girl?
• There was a (history?) teacher who the girl liked, but he turned out to be evil. Or something.
• There was a special book and a bunch of potions, "magic" done with various plant based matter

Other than that, I can't remember anything about it, since my memory is weirdly selective.

Answer 1

The Apothecary by Maile Meloy. The book is called "The Pharmacopoeia". Mr. Danby is the Latin teacher who might be a spy, or a double agent.

Amazon summary:

When Benjamin's father is kidnapped, Janie and Benjamin must uncover the secrets of the apothecary's sacred book, the Pharmacopoeia, in order to find him, all while keeping it out of the hands of their enemies - Russian spies in possession of nuclear weapons. Discovering and testing potions they never believed could exist, Janie and Benjamin embark on a dangerous race to save the apothecary and prevent impending disaster.

And one of the potions turns the children into birds.