be on a mission

1. To be in pursuit of some specific duty or ambition, especially that which is of particular importance, significance, or seriousness. The spies vanished from public life for months while on a mission to uncover who had bombed the state building. Our company is on a mission to help those less fortunate. That's why we've created a series of new volunteer programs in our local communities. We are on a mission to find out what really happened that day, so we can bring closure to the families of the dead.

2. To be fiercely determined to do or get what one wants. Oh, after I heard how much that slacker Jim makes, I was on a mission—I stormed straight into my boss's office and demanded a raise. When my boyfriend decides he wants to buy something, he's on a mission until he has it in his hands. I don't know why Dad is suddenly a man on a mission to clean out the garage, but I have no objections to it!