The party led their prisoner goblin through a secret passageway in the pantry toward the supposed prison in the basement. At the foot of the stairs was a trap door leading to a pit with spikes and venemous snakes. Shaylem was able to climb across safely to the other side and throw a rope across to Harlan and Oscar. Oliver stayed on the other side to guard the goblin and Charlie (NPCed) stayed up in the kitchen as a look out.
Heading down the hall, a Yuan-Ti snuck out of a hiding place and tried to attack Harlan from behind, but Harlan reacted more quickly and was able to get the first attack in. After several rounds of battle, the Yuan-Ti was defeated but Harlan was knocked unconscious. The goblin also tried to escape and after a struggle, Oliver pushed him into the pit.
At the end of the hall there was an iron door. Shaylem successfully hit it with acid splash and was able to open it. Inside the group found six even prisoners and the dragonborn spy they were sent to rescue. The dragonborn revealed himself as actually being Oof Duh (as the whole party suspected all along!)
Back up the stairs, one more Yuan-Ti was in battle with Charlie. They defeated it and Oscar took the creature’s Flame Tongue sword. The party searched the rest of the mansion to discover sets of quickly built bunk beds upstairs, a room of armor and weapons for at least an army of 40, and 50 gold pieces each in treasure. The elves explained to the party that the mansion has been taken over by the Pomarj as a stronghold to keep troops and to build up their army for invasion of Two Ford.
They loaded up the wagon with the armor and weapons to bring back to the elven resistance and took a long rest.