Christmas dinner is interrupted by a phone call from the plant, where engineers are working. Karen listens in. She then has an ominous meeting with the Americans.

We have a look at two important medieval manuscripts in the State Archives. They are the original Constitution of the Republic of Siena. Alberto Angela gives us some fascinating facts concerning it that reaffirm how wise the rulers of that republic were.

The contents of the blue backpack point to a possible motive. Luca talks to his sister again, but she is still visibly upset, which is understandable. Marta finally talks to Luca about what has been weighing on her for a while.

Lorenzo is seriously upset with his mother. He wants to be left alone, but Eva has a hard time with that. On a different front, Eva goes to see Augusto for advice and help regarding the mechanic.

The protest at school continues, and there is tension among the teachers and the principal. At home, Renzo has a first encounter with the housekeeper. He finds her a bit odd.

Martino makes an important decision, but gets stopped in his tracks. He's going to have to change his plans.

Karen sends a clear message to Adriano and they meet. She has something important to tell him.

Arianna prepares the ingredients for the panzanella and stresses that this recipe is easily adaptable to personal tastes. You can't really go wrong. It's also a great recipe for anyone to make while vacationing in Italy, since it's so simple.

Luca goes to see Ginevra about the autopsy, but he confides in her, too. Toscani is having trouble telling Luca the results of his investigation into the passengers of the bus.

The girls carry out the first part of their plan. They see that the mechanic has plenty of work and plenty of money.

Little Livia is in the backseat as her mom drives another teacher home. She listens, she opens her mouth when she shouldn't, she observes. She draws her conclusions and then bets on them with her mom.

Martino has a hard time accepting what the priest and police have come to tell him. He's stuck.

Mauro gets a political slap in the face. Olivetti is undergoing huge financial challenges and risks going under but Adriano doesn't lose hope.

How could accounting books be so fascinating? The ones from the State Archives in Siena are veritable works of art and tell some interesting stories.

Luca is very upset with his sister. He feels betrayed and starts getting really worried, both for her and for himself, since he has gone out on a limb for her. The investigation continues.