In the Kingdom of Cruor, magic ensures that each Queen gives birth to twins: an heir and a spare. Simply by existing, the spare is believed to protect their sibling and over the past centuries has always died first, whether by illness, violence or some other misfortune.
But myth is about to be challenged: the current heir dies on a frosty mountain-side, throwing Cruor into upheaval. The young spare - who has never been spoken to, educated, or loved - is thrust into the public eye. His father, the King, resents him for living in place of his brother and society thinks he's an unfortunate freak.
Then the royal mage discovers the spare's hidden powers. Other citizens bleed from the palm when they magic. The spare can do it invisibly - and now malevolent politicians want to use him as an assassin...
this is a hook.
I don't read enough science fiction to know if it's over used or cliche or been done to death, but this is a hook.