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Talk to Evennia and she will give you the Scepter.

A player holding the Scepter will gain +1 energy regeneration.
If dropped on the ground, it generates the Scepter of Orr's Aura around it that gives all nearby allies +10 maximum energy.
You must deliver the Scepter to Vizier Khilbron, who will appear when you arrive at the ancient monastery, located on top of the cliffs. Follow the path shown on the map. After your rendez-vous, the Vizier will instruct you to go east, towards the docks (marked B on the map). Once there you will have to protect him while he summons a ship from the depths.

The fight that will ensue between you and the White Mantle that will come from the north and south and try to stop the Vizier from performing the summoning can get overwhelming and is the hardest part of the mission. They mostly come in pairs, though one pair is accompanied by a boss fairly early on.

When the ship is finally afloat, go aboard to finish the mission. Only one party member has to be alive to complete the mission, so you may want to focus on survival later into the battle. You must also protect the Vizier. Try to battle just before the pier and keep the Vizier out of aggro range, so the chance of a Mantle turning to attack him is smaller.

The boat will open for players to jump on three minutes after the end sequence of protecting Vizier Khilbron begins. Six minutes after the start, you will be attacked by ten White Mantle at once--five from each direction. These are the last White Mantle that will come attack, so if you can clear them, you can then safely abandon Khilbron to finish the bonus or explore the beach.

Bonus
Find the Restless Spirit that loiters around the rock on the beach (marked 1 on the map). Talk to him while holding the Scepter and he will follow you. He will stop walking when the scepter is dropped on the ground. Your goal at this time is to bring him to the Vizier.

Once you've delivered the Scepter to the Vizier, you have to wait a moment after the end of the cutscene and talk to the spirit again once you see a green exclamation mark. That will make the spirit follow you once again. Your task now, is to lead him to a graveyard (marked 2 on the map).

Follow the path until the Vizier appears for the third time. Stick to the right mountain wall as much as you can. Doing so, will omit the Vizier from appearing at the docks, giving you ample time to get the spirit to the grave and finish the bonus. Do not linger however, since the White Mantle will already start running toward the pier, and the Vizier can be swarmed. Get the spirit to safety and run back quick, unless of course you don't care about finishing the mission. Alternatively you can split up so that one person saves the spirit, while the others keep the Mantle busy. You can also try to use the fact that the Mantle group up on the pier to your advantage. They are a great target for any strong AoE Spells if there is someone that can heal the Vizier while he gets attacked. If done right, you can kill off the large group and then defend the pier as usual.

A relatively simple way is to just have the whole party take the brunt of the Mantle assault as normal, but not getting on the boat. The mission won't end until a party member enters the boat, so the bonus can simply be done after the boat is summoned. Be advised that there still can be some Mantle coming afterwards, which could kill the vizier anyway. Keep an eye out for this.

A major problem with this strategy is figuring out exactly who the Spirit is following.

Mission and bonus together
Doing the mission and the bonus in the same run is much harder than just doing one or the other. There are several approaches that can work.

The direct approach
When you get to the beach, go down to make the vizier spawn, and stay in front of him to defend him. Kill all of the mobs as they come. At the six minute mark, ten mobs will come at a time, five from each direction. Kill all of these, and no more white mantle will come, so you can safely leave Khilbron alone while you complete the bonus. This approach has the advantage that if you start to get overwhelmed past the three minute mark (especially when the ten come at once), you can get on the boat to abandon the bonus and at least get credit for the mission.

Bonus first
Bring lots of heavy area of effect damage skills and some potent single-target heals. When you get to the end part, stay away from the beach and go do the bonus. Come back to the dock and run in to save Khilbron. Launch whatever heavy damage skills you have, and throw the vizier some heals. Kill all of the white mantle quickly taking advantage of them being bunched up, and fight off whatever else comes for the next three minutes until the boat comes. You need far more firepower to pull this off than to merely beat the mission, but it does pretty much guarantee you the bonus. Don't try this in hard mode.

Let heroes defend
If you are alone except for heroes and henchmen, you can flag them in front of the dock to kill whatever comes while you head off to complete the bonus on your own. Spread them out a bit so that they don't all get nuked by Searing Heat. You can run past the few mobs you see, and they won't attack the restless spirit. After finishing the bonus, head back to the dock to help out. Don't try this unless you have heroes of much higher level than the mission intended (which is impossible in hard mode) or they'll get killed.

Split the ten
Stay away from the dock to prevent Khilbron from spawning, but close enough to grab any white mantle that come. You may have to use flags to hold back heroes and henchmen. Kill any mobs that come until ten come at once at the six minute mark. At this point, run either north or south to grab one group of five, while letting the other five proceed to the dock unimpeded. Kill the five you've chosen, and then do the bonus. Come back to the dock and save Khilbron from the five mobs clustered there, and then wait three minutes for the boat to arrive to complete the mission. If you start to get overwhelmed as mobs are still coming, then just run away and wait for all the mobs to get to the dock, then go do the bonus, so that you don't end up with nothing.

Flatbow pulling
Go do the bonus first, and then stay out of the way until all mobs cluster on the dock. Flag your party far back, and head north of the dock with a flatbow or longbow. Attack something on the dock and your character will run toward the dock, press against a ledge a bit, and fire off a shot far enough away that Khilbron won't spawn. Run away and see what comes. Repeat as necessary to get something to come, but few enough to be a manageable battle. Do this however many times it takes to clear the dock, then get on the dock and wait three minutes for the boat to arrive.