The background is that one of the characters in the campaign, has some major bodily damage, beyond the capabilities of the party to heal. They rush him to town to find a healer.
The healer heals the character, but tells the party that it is only temporary. He says that the character will need the application of a special herb to make the healing permanent. The healer tells the party how to find a Druid whom he knows for the whereabouts of the herb. The party is able to get the Druid to agree to accompany them.
The Druid knows the general area in which the herb grows. Finding the herb is not a guarantee. After a trip taking several days into the outback, and approximately one day of unsuccessful searching for the herb, the party has an encounter with a group of orcs. (Party ambushes orcs, orcs ambush party, whatever). When searched, at least one of the orcs will have a small quanity of herb on his person. If all the orcs are dead the party will be able to track the orcs to their 'lair'. If one is alive, he will bring the party to the 'lair' if threatened. If asked about the herb, the orc is not aware that it is anything special. (The orcs gather quantities of the herb and use it as a narcotic and are unaware of the herb's healing powers, as they smoke it - not the proper form of application. If any orcs are questioned about the herb, treat it as if someone on the street beat you up, took your cigarettes and asked about their 'special healing properties'.)
The orc 'lair' is actually a small village/outpost. If this region is orc infested, make it a village (they have to come from somewhere). If the region is relatively orc-free, have it an advanced orc outpost. (i.e. no non-combatants)
Have enough orcs in the 'lair' such that a frontal assualt would be nearly impossible. Sneakiness counts here folks!
The 'lair' is actually above ground. It consists of a group of huts sufficent for the orcs' purpose. (Housing, maybe a forge, food, armory,
etc.) Two of the structures will be made of stone, the places occupied by the priests and the high leaders. The entire village is surrounded by a wooden palisade. (Think of old forts in western movies.) The logs are buried deep enough so that they cannot be easily moved. The wall is nine feet high with points at the top, and is treated with a sap-like residue from the local trees that make it nearly resistant to fire. (Fires take more time to start and don't spread fast.) The walls are not tough to climb by oneself and are easy with the help of another. Within the walls are several outpost towers (approx. 15 feet tall) that are used to see out beyond the walls.
The orcs have enough of the herb to take care of the injured character, plus possibly some left over for the party.
For combatants, remember that in an organization this size there will be a chain of command. I had a supreme leader, a second in command, a handful of lieutenants, many sergeants and about 150 standard fighters. I also used two spell-users to make things more lively (players occasionally fall into the trap in which they believe they are the only ones with magic accessible to them) and an ogre to make things exciting. I also included 20 worgs in a pen. (Worgs are large semi-intelligent, evil wolves that orcs occasionally ride into battle, also called dire wolves.) The worgs will only affect the outcome if either released from the pen or if the party tries to sneak by them.
If any of the party escape and at least one of the others are captured, one of the spell-users will attempt to charm the character. Once charmed the character will be instructed to find the rest of the group and bring them back to 'rescue' their comrades. (This is a -great- chance for roleplaying for the the player involved!) Set up an appropriate ambush. If the orcs' plan to entice the players back seems to have too many holes in it, that's ok, orcs aren't renowned for their great plans.
The herb, in addition to its healing properties is also addictive. For healing, the herb must be administered over a one week period. In games terms, withdrawal from the herb will result in a penalty to action. Withdrawal will be complete five days after the last time the herb was administered. During these five days, the penalties should peak at day three then gradually drop off. Since the herb has a side-effect (withdrawal), races that have a natural resistance to poison will not benefit fully from the herb.