Gaining access to the Theater of Blood (also known as the Plane of Music) is the first hurdle in PoR. Your quest begins in Arcstone with Arch Mage Galsin. He can be found near the zone entrance. Speak with him and he gives a bit of background about ToB and tells you that Ao the Fourth Born has been looking for a certain book, and this book just might have information you need.
You'll find Spirit of Ao the Fourth Born on the western side of Arcstone, near the portal entrance to Relic. Talking with him reveals the book is the Codex Artifice. He sends you on a sequence of three tasks:
Upon completition of the third task, you receive a Harmonic Chime. Take this back to Galsin and speak with him. Turn in the Chime and he gives you a Silent Harmonic Chime. It appears that something has corrupted the Chime and it no longer gives off the sound needed to port to ToB. The original Chimes had be destroyed by Sullon, so a member of her domain should be able to work with the Chime and hopefully restore it. This leads you to The Devastation, and Oathmir the Outcast.
Oathmir the Outcast says he can help, but we must do him a favor first. It seems that the rage of Sullon has felt corrupted as well, and Oathmir wants you to first figure out how to enter the tower, and then go find out whats wrong.
The progression starts with the Saga Skins mission. Completing this initiates the Preparing your new skins single person task. Once that is finished you return to Maelin and say "become the vessel" to kick off the group task, Become the Vessel. The reward for BtV is an Enraged Flesh Charm, which goes on your keyring, flagging you for entry into Razorthorn (the Tower of Sullon Zek). If you join a group doing Vessel, you can get the Charm without having completed skins or the preparing steps. Once you have the Charm, return to Oathmir. He will now offer the Samples of Corruption task. Finally, after collecting the samples, Oathmir will agree to work your Chime. Hand it in to receive Twisted Chime. You can join a group doing the Samples task without having the Charm, and once completed Oathmir will talk to you (although, you'll need the charm down the road anyway)
Back to Galsin and show him the Twisted Chime. He returns it to you (different id, so you need to do this step) and informs you that while the Chime is indeed modified physically, it no longer has the magic enchantments it needs. The royal family in Eldaar had the knowledge of how to do the enchantments, so you need to locate on of them. The journey moves to Northern Ro.
In the Northern Desert of Ro we find Tak`Valnakor. He's an archeologist looking into a servant of the old royal bloodline. He sends us on a series of three missions, which culminates in us aiding the Queen:
Completing the three steps earns the Queens favor. Ask her "What about my Twisted Chime" and she says she'll show her gratitude by working the magic. Hand it in and receive a Twisted Harmonic Charm in return. Back to Galsin!
Give Galsin the Chime and he finished the story. You gain an AA called "Harmonic Dissonance" which lets you port to Theater of Blood (15 min reuse). You are now flagged for ToB.