there will be hell to pay

When someone says there will be hell to pay they mean to say that they are very angry at something that has just happened and that when they find out who did this thing, they plan to punish them. By saying there will be hell to pay, this person means to hint that they will be going through hell, such as through verbal or physical punishment. It is usually spoken to a third party, not necessarily the person who has done the wrong thing.