The quest starts with the NPCs at 43.7N, 54.9E. Far Claw Villas out of Arwic is the closest settlement. There a lifestone closer to the NPCs at 48.3N, 57.4E. There is also the Olthoi Tunnels dungeon at 48N, 53E. Speak with Adrien Swiftblade to start the quest.

Adrien Swiftblade tells you, "Greetings. If you're of a mind to help in this odd situation, I could certainly use your help."
Adrien Swiftblade tells you, "Along with the rise of these strange new Olthoi, there is a Portal, warded by powerful magics, which formed in the Black Death Catacombs. You may've seen it already, or you may not have."
Adrien Swiftblade tells you, "Anyways, I've found a way to get the wards to drop for a time. There is a Ward Guardian in a cave located in a heavily infested area nearby, around 43.6N, 55.5E. When that thing dies, the wards falter for a time."
Adrien Swiftblade tells you, "Once the Ward Guardian is dead, so you should be able to enter the Deeper Catacombs of the Paradox-touched Olthoi. Once in there, look for anything that may be of use to use in our research and bring it back to me."
Adrien Swiftblade tells you, "If, for some reason, the Portal is closed again when you get there, you should find the Ward Guardian in his cave and kill him again."
Adrien Swiftblade tells you, "I would hurry though, every time the Ward Guardian dies, it's either reborn, recreated, or whatever roughly six hours after its death, and the Wards return with it."

Head down into the paradox-olthoi invested valet below. There are three hive entrances dug into the ground. Two of them lead to the same dungeon, the only thing inside of interest is an olthoi door that cannot be opened. To reach the Ward Guardian, you will want to take the most southern hive entrance in the valley. Inside is quite a maze, but eventually you will come to a long hallway winding upwards which leads to the Ward Guardian's chamber. Kill the Guardian and a global will be broadcast:

As An Adventurer strikes the final blow on the Paradox-touched Olthoi Ward Guardian Nymph, a high-pitched keening echoes through you mind. You feel, rather than know that the wards around the Paradox-touched Olthoi Queen's portal have failed for the time being.

You are now ready to head to the Black Death Catacombs (BDC). It can be reached two ways: If your allegiance mansion has the olthoi lands portalling device, one of the locations it can send you to is the BDC. If you don't have access to this device, head to the Hebian-to settlement portals (around 41.5S, 82.2E) and take the Arrowdale Cottages portal. The BDC is a short run away at 60N, 71.1E.

Once inside the BDC, you'll want to head to the paradox-hive portal. It is in a room off the entrance area - the only hallway opening on a wall and not on the floor. With the wards down you can now enter the portal. This dungeon is fairly easy to navigate. You will have to run across two acid pits total. After the second pit there is one split in the hallway. Take the left hall. When you reach the bottom there will be several Paradox-touched Olthoi Eggs on the floor (timer to pick up: 13 days).

In this final room there is an olthoi door that cannot be opened. If you attempt to open the door, the following message appears, "As the door is touched, it emits a high-pitched keening sound, alerting the local Olthoi to the presence of an intruder." This will spawn two Paradox-touched Olthoi Noble Nymphs in nearby streams of portal energy.

Return to Adrien Swiftblade for your reward:

You give Adrien Swiftblade Paradox-touched Olthoi Egg.
Adrien Swiftblade tells you, "An Olthoi egg?"
You explain to Adrien Swiftblade the circumstances of the catacombs and of the egg room.
Adrien Swiftblade tells you, "Damn. So, it seems this new threat is one that won't go away lightly. Nothing is ever simple in this world."
Adrien Swiftblade tells you, "I'll send this along to our researchers. Perhaps, with time and effort, we can find out where these new Olthoi came from, and find a way to put a stop to them before the threat they pose grows worse."
Adrien Swiftblade tells you, "You've done this world a great service today. Please, allow me to reward you for your efforts."
You've earned 18,397,757 experience.

Adrien Swiftblade tells you, "Thank you again. The egg you have provided us should keep the Researchers busy for a while. They don't seem to keep well away from their cave though, so they tend to lose their usefulness in two weeks after you take it from the catacombs. So, if you're interested in helping us again, return then."