To understand the events at the Valerius' villa, one most know what happened there years prior. By putting together the information they can gather in the villa, the party may be able to put this story, or at least parts of it, together.
While the Valerius family has weathered the storm of Rome falling and various Germanic tribes conquest well so far, they are in decline both politically and economically. The dance of ensuring to be in the good graces of whoever rules currently was becoming more and more difficult, and the various business ventures were drying up one after the other.
Among all this, the family was breaking apart with Lucius' father demanding more from his sons and growing increasingly unhappy with their failure to boost up the family fortunes. As a consequence, conflicts within the family have been tearing it apart for years.
Lucius, the oldest son, especially squandered what we left of the family fortunes, with risky and stupid investments, luxurious lifestyle and the occasional misfortune and run-ins with the new law that had to be smoothed over with hard cash.
The fire was not an accident. It was Lucius who torched the villa in rage when his father disowned him. He has been haunted ever since and is in shame and denial. On some days because he truly regrets killing most of his family, on other days because he just wanted to murder his parents, not burn down the entire villa.
After the fire, Lucius fled the area. He had put some money aside and could turn some of his useless spending into cash (e.g. by borrowing from the same people, never intending to pay them back), and from this money could live for a few years, but now money is running out.