Dastan marches directly to the guards at the gate, making sure that Trinia and the others follow close behind. He stops just short of the blonde-haired Commander and raises his fist to his chest. He announces quietly but matter-of-factly, "Good afternoon, Commander. My companions and I are escorting this woman out of the city for her protection; we believe that a group of criminals wish her dead. It is of the utmost importance that she reach safety before the group in question learns of her presence, and we've arranged for... Allies to meet us not far from here to take her someplace safe until the danger dies down. May we pass through?"

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There, that looks like the right blend of truth. Take out the details and it sounds like the sort of thing Paladins are supposed to do all the time, doesn't it?

Diplomacy: (1d20+15)[19], plus any modifiers gained from Aid Another, spells or what have you provided by the others.