The Seven-Pillared Hall plays home to several subterranean trading cartels; one of them is the Deepgem Company, owned by the dwarven cleric Ulthand Deepgem.
Recently one of Ulthand's mining expeditions was slaughtered by unknown assailants, and their beast of burden - a dire boar Ulthand had raised as a family pet from childhood - was stolen. A lesser dwarf would want revenge on the monsters that killed his friends and employees but Ulthand will settle for having his pig returned. It's a quest he's not shy handing out to anyone who asks him about the glowing yellow exclamation mark above his head.
Ulthand's boar has, in fact, been captured by gnolls. It's not clear why the gnolls would kill a dwarven mining expedition but leave their (clearly dangerous) pack beast alive, but they have, and the boar now serves as a target in a cruel kind of gnoll archery practice.
Players entering the Practice Hall find the boar penned into a crude enclosure, surrounded by hyenas. Gnoll archers hiding behind a clumsy barricade take turns firing stinging arrows into its side.
There's a wonderful kind of double standard at play here. It's unclear whether the module designers really thought this one through but the dialogue they're expecting from players must run along the lines of, "Animal cruelty! That's awful! Let's bash the skulls of these hyenas in so that we can free that poor pig!"
We'd probably better assume that pigs are more endearing animals than hyenas and move along to the combat. There's an oddity here created by the battlemap. Obviously the major terrain feature is the barricade separating the gnolls from the players (who enter from the north end of the map). Getting into melee with the gnolls seems to require charging and climbing over the barricade.
What's not shown on the battlemap is a corridor linking the doors in the northeast with the doors in the southeast. Players leaving the map at the north end can take a leisurely stroll through the adjacent tunnels and ambush the gnolls from behind, driving them up against their own barricade and easily defeating them.
It's a good example of how what the DM chooses to depict or not depict on a battlemap can focus players' thinking in unrealistic ways. DMs need to remember that players aren't operating in a perfectly rational universe; they're vastly guided by the way DMs present the game, and by altering that presentation DMs can alter players' actions.
In any case once the gnolls and their hyenas are dead, players are left with the issue of the boar. It's half-mad from the abuse it's suffered and if players want to get it back to Ulthand and complete the sidequest they'll need to calm it down. Doing so involves the horrible skill challenge mechanic but neverthless it's the kind of thing I wish Thunderspire had more of. It's a dramatic change of pace from the tactics and room-clearing we've had up until now and it appeals to types of player who Thunderspire has previous overlooked.
If players are successful with the skill challenge they end up with a dire boar following them around. That's awesome. There's a problem, though - the remainder of the Well of Demons is ill-suited to the presence of a large nervous animal. Player are either going to have to chain the boar up in one of these entry rooms, turn around and take it back to the Seven-Pillared Hall, or play the remainder of the dungeon with a noisy ill-tempered wildcard at their side.
Notes and Improvements:
 The barricade used by the gnolls is, as-written, hay bales. Really? Hay? What, did they import that from the surface just in case they happened to steal a dire boar? I'm not a farmer, but do pigs even eat hay? It doesn't make sense and you should probably change it to either loose rubble or broken furniture.
 The flavour text for the room contains a troubling detail - murals show minotaurs fighting other minotaurs, and the text makes a point of emphasising the minotaurs are unarmed. Knowing the Labyrinth's backstory it's clearly just intended as history but it's irrelevant history. Players, assuming they wouldn't be shown something like this unless it was in some way relevant, may be inclined to think going unarmed is the solution to a future puzzle. It's not, and you should probably take the time to make that clear here.
 The Dire Boar is not just a monster, it's also a mount. Players with the relevant feat to unlock a mount's special abilities will discover the Dire Boar's mount power is the awesome furious charge - an eight square charge dealing 1d10+9 damage, pushing the target two squares and knocking them prone, and following up with a further 1d10+9 gore attack. It's a great way of demonstrating how useful mounts can be, so if no-one in the party has the relevant feat DMs may wish to give players who choose to ride the boar a "freebie", allowing them to try out the furious charge for one battle as a kind of introduction to the mount rules.