Celia is the daughter of a famous illusionist magician Hector Bowen, and Marco is the adopted apprentice of a less frivolous, but equally skilled Mr. A.H. (commonly referred to as 'the man in the grey suit'). Bowen and Mr. A.H. have always had a different opinion about their magic, and thus have set their two students into a competition to demonstrate which school of magic is better.
Le Cirque des Rêves
“Secrets have power. And that power diminishes when they are shared, so they are best kept and kept well. Sharing secrets, real secrets, important ones, with even one other person, will change them. Writing them down is worse, because who can tell how many eyes might see them inscribed on paper, no matter how careful you might be with it. So it's really best to keep your secrets when you have them, for their own good, as well as yours.” -- The Night Circus, Erin Morgenstern