duty calls
(idiomatic) Expresses that the speaker must go and deal with something.
Excuse me, gentlemen, but I'm afraid duty calls.
There's no urgency, a third voice urged, pleading compromise. No duty calls. Hold onto the illusion a little longer. So she tried to go on pretending. After all, can't believing sometimes make dreams come true? No, it can't. Besides, you're awake now. David Brin
He has no right to his life when his duty calls him to resign it. Other men are bound... to deprive him of life or liberty, if that should appear in any case to be indispensably necessary to prevent a greater evil. William Godwin