anyone have any ideas for my book?.....

ok i need some help im stuck..... and need some good ideas for my book.........heres what its adout.........

ok so there's 3 kids(all girls) there names are....... kara she's 14teen,cody she's also 14teen, and sallie she's 13teen.....so one day thay find this notebook and open it up, its adressed to them... it said bewarnd for darkness is comeing in the shape of a boy....one of you will turn...one will run and hide... the one left can save it all... if they dare to try....

thats all i got have anygood ideas.....
please help.....