Introduction
The adventurers obviously hadn't come up with a usable plan to neutralize the attackers, so they decided to postpone the issue. First, they scouted the farm facilities using the psi powers of the knight, and decided to go treasure hunting instead of fighting. In Ulayah's bedchamber, under the bed, they found the buried profits of the spider farm. And yes, it's totally fine to start digging in an abandoned house in the middle of an enemy compound.
Battle... slaughter...
The knight and the barbarian were digging, while the assassin hid in the entrance room. Soon enough, a couple of armed men came over. It looked like Ulayah finally broke to the torture, and spilled his secrets. The adventurers successfully cornered the bandits.
The knight discovered how to effectively use an invisibility spell. I, on the other hand, had employed lots of armed opponents, and compensated for their number by making them relatively untrained, undisciplined thieves instead of hardened soldiers. The invisible knight thus proceeded to slaughter a bunch of unprepared, helpless men.
Shamil decided to drink an invincibility potion bought from an old gypsy woman. Mild side effects included the inability to speak. Any attempt to do so made bubbles burst from his mouth.
Invisible or invincible, the adventurers easily muscled their way through the attackers. None of them escaped, but the sounds of the fighting were soon heard in the courtyard...
And the adventurers were confronted by the full band of killers!
Of course, it barely took a couple of turns for them to see their own helplessness. They turned around, screaming wildly, and ran away. The boss tried to salvage the situation by keeping Heri as hostage... but that was no obstacle for the invisible knight!
He chopped off the arm holding a dagger. Just in time for the enraged barbarian to get there, and pulverize the remains of the man.
Besides the thieves who had ran away, there was a single survivor - a warlock captured during the first confrontation, in the living room. Shamil started torturing him. His defiance cost the captive his left arm, and soon he revealed all he knew about the situation - he was in the employ of the foreign thieves' guild known as the Cobras, and they tried to gain control of the spider farm. The adventurers let him escape, so as to deliver a message to his masters about the invincibility of their opponents.
Conclusion
After all that action, the adventurers were quick to turn the events in their favor. They kept the treasure, and let Ulayah believe that it was taken by the attackers. The cornered entrepreneur was then easily convinced to abandon his principles, and join whatever organisation offered him and his daughter protection.