What the tone of the book The Red Pyramid by Rick Riordan?

The main characters' (Sadie and Carter Kane) mom died and they had to be separated at age six. (Sadie with grandparents and Carter with dad) Since then, their dad has been gloomy and looking for a way to "Set things right".

At a museum, Mr. Kane tries a spell to bring his wife back to life, but just ends up more trouble, but this time, Mr. Kane is trapped too

And that's just the main problem, if you want more detailed problems, the book has loads of them!

The main problem is Carter and Sadie trying to defeat Set and to release Uncle Amos from Set's possession. Unlike what that guy said. ^^^^^^^ :P