As Arin wanders about the house, she finds herself in the store room, and from there, a bit of light shines through the wall from Helmdos' bed chamber. She can easily see into that other room, onto Ashe and Vargo as they begin to rummage through that room and the study.
Saxon and Marcus, Ms. Cavrandale leads you into the kitchen, where she lifts a small trap door. A few layers of damp cloth conceal the unmistakeable odor of a sewer- its tunnel is about ten feet below this trap door, and there is a wet, slippery-looking iron ladder bolted to the edge of the tunnel. The sewer smells salty, as if it connects to the sea, and the water in half-pipe in the middle of the tunnel is flowing very fast to the southeast.
Vargo, you and Ashe converge on the bedroom and study and begin basically tearing it apart. Ms. Cavrandale enters shortly after showing Saxon and Marcus the sewer entrance, clucks to herself, and begins to tidy up after you.
A few moments later finds Arin joining you in your search, and between the three of you, you find a journal sitting in the reading stand of Helmdos' bedroom. Intriguingly, it mentions something about two men named E. and U. coming to visit Helmdos the day before his disappearance. While Helmdos writes that these two men "were as brothers to me", he bid them leave his home and not return, and seemed sad that "my time with the society is at an end". In Helmdos' study, buried in the reams of tax information and records, you see that Helmdos was an adherent of Maslan the Shield's faith, the protector god of Gavar itself. His "temple dues" are exorbitant- he was paying 3% of his income in the months before his disappearance.
Finally, hidden beneath Helmdos' mattress is a signet ring. It bears a plain white face (probably alabaster) with a raised, stylized letter "I" as its insignia.