I'm only half-way through, but thought I'd get started.
First things first, I now know where SRD came up with the Ravers (even if he doesn't, and he insists it was only his subconscious that caused him to borrow them from RZ
Don't get me started on where he *cough*stole*cough* Holt Fasner's invalid mother.). Okay, so Sam travels to the Hellwell to release a pack of demons that he bound up a hundred or so years earlier. He makes a deal with the lead demon, Taraka, letting him free in exchange for the secrets to invade the Celestial City. Taraka agrees, and at first seems to keep up the deal. We learn some cool stuff about the CC: it's not really Heaven (duh!), but some sort of elevated domed city with elevators and portals that allow spaceships to enter and exit. Anyway, after a couple days, Taraka double-crosses Sam, and while Sam is sleeping, he possesses him in full-on Raver-style. Seriously, it's exactly the same thing. He then goes on a drunken frat-boy rampage, which Sam actually agrees totally kicks ass. The two of them bag milfs for a few weeks in Sam's palace, but some of the other demons do freaky stuff, like re-animate corpses and then get it on with each other. Life is tough when you're a demon bound for eternity in the Hellwell, so you get it anyway you can.
Sam tries to defeat Taraka a few times, but can't do it. Finally, he channels his inner mother-in-law and makes the T-man feel guilty as hell for all of his drunken debauchery, and guess what? It works. Taraka agrees to get back to the business of kicking god ass.
Next, a certain Lord Agni comes in search of Sam. He's the lord of fire, and he uses his fire wand to torch a bunch of demons. He was given the wand from Yama. It's pretty clear the wand is really some sort of laser cannon, but most of the characters in these books consider technology to be magic. Sam wants to run like a schoolgirl, but Taraka insists that they take on Agni, because he knows if their body gets torched, he can just take off in his spirit-form, and he tells Sam that he'll bring him along for the ride until he can find another human body. Long story short, fighting Agni turned out to be a bad idea. Sam and Taraka escape back to the Hellwell. Their reprieve is temporary, as Agni takes a Chariot to the gates of the Hellwell along with Shiva, Kali and Yama to root out Sam. They beat up on a bunch of demons, but Sam and Taraka manage to escape and they head for the chariot. They get to the chariot just in time, but Sam apparently isn't used to driving a manual, and forgets that he has to step on the clutch to start up the engine. So while he's screwing around, Yama and Kali show up an lower the boom on him. Taraka bails, and Sam is screwed.
Since the "demons" are an energy life form, this is how he was able to trap and bind them when the humans first came to the planet. 