Scene summaries may contain spoilers
Samnium meets you at a fort, and tells you that he has a letter with the Emperor's seal that you both need to deliver to Aeneas. Aeneas is getting ready to march on the Pictish, but it's not safe to travel to his encampment alone, so you'll stop at the barracks to meet Petronius, a guard soon retiring who will join you both on your delivery run.
You meet up with Petronius. Sam reveals to you that he opened the letter and discovered that the Emperor is ordering Aeneas to call off the fighting, and to let the Pictish have their side of the wall. Sam is very pleased by this, but thinks Aeneas won't be. You'll all follow the tributaries that will lead you past the prison camp, towards Aeneas.
You arrive at the prison camp. Petronius and Sam discuss the barbaric treatment of the Pictish, and how, since Aeneas was put in charge, the treatment of them has gotten much worse. Neither of them like this side of Rome.
Aeneas is moving a lot of troops, so you have to move quickly. Sam wants to give a proper burial to the Picts who have been hung by the gate, in full view of the other side of the wall, where Picts might see and end the peace talks. Petronius reminds him that you don't have time. After you've cut them down, he promises to send someone back to bury them, because time is of the essence.
You've cut through a valley to get to Aeneas quicker, and Sam and Petronius describe how the Pictish side of the wall is so much wilder and more natural. They point out the highly poisonous flowers, which Aeneas gleefully uses to kill so-called traitors. But you're on the move again once you spot a Pictish raiding party, who send arrows flying. You need to get back behind the wall quickly and hope they miss!
You arrive at Aeneas' encampment, which is like a city of tents. Sam realises that Aeneas has armed the cooks, which doesn't augur well -- this will be a bloodbath if a war breaks out. Petronius spots Aeneas' bathhouse, imported brick-by-brick from Rome, and you all head towards it, quick as you can.
In the bathhouse, Sam delivers the message to Aeneas. Aeneas responds by ripping up the letter and saying he will not obey, and Sam doesn't know what to do... So he arrests Aeneas and has you gag him. Now you need to get to the Picts, and fast.