City of bones

I'm talk about the book of city of bones by Cassandra Clare 

When fifteen years Clary Fray  heads out to the pandemonium with his friend simon, she began to follow a attractive boy with a blue hair, but what she can not imagine it is going to witness a murder committed by a three teenagers but she is the only that view the murder, because is something that mundanes don't can view. Since then the life of Clary change then the teenagers explain that they are Shadow-hunters and protect the people of the demons after that Clary's mother disappears and she, simon and they go to find his mother