Rift Quest:Consequences of Neglect  

Yes, you're instincts are correct. When you activate the beacon something ugly will appear and attack you.

The first to appear will be the Necrotic Gatekeeper (44) who will draw a great, big summoning circle on the ground and call for his minions. He is not attackable, or even targetable, at this time so sit back and watch.

The minions (43) will come in waves of 1 to 3, ending when the Gatekeeper announces that he is just going to kill you himself. He does not seem too interested in waiting so you will likely still have the last wave of minions to finish at the same time.

If you fail on Azen, the next try you will face only a single wave before the Gatekeeper attacks.