Below you will find a short summary of certain milestones in the story of Isle of Artaeum. If you’re not sure how to progress in the story this can help you find your way. Take care not to read too far ahead though as each section will contain spoilers.

Arriving at Isle Artaeum

Once you have completed the College of Winterhold questline a Psijic Messenger will await you in Winterhold village. After that you can travel via an enchanted boat, that’s docked outside Solitude, to Artaeum.

Starting the main adventure

Once you get to Artaeum, you will see a familiar sight. By The Eye of Magnus the Psijic’s main researcher, Gynthar, will ask you to assist him with his studies. Help him find out more about the mystery of Magnus.

Getting to Auridon

After learning about the threat of Magnus Gynthar decides to gather up the available Psijic council members, also known as Pillars. In order to get them all in one place Auridon and Artaeum is conjoined.
Go meet Ju-Lihen, in Dawnstar, and she will show you the way to the island of Auridon.

Going on after Magnus

When the Psijic Council is gathered you’ll learn about the insippient threat of a pirate invasion. A spy was caught inside the council chambers and Ofelia, the Master of Auridon, will ask for your assistance.
Trick the pirate into thinking he will escape, and find out why the pirates are attacking the Psijics.

Joining the Psijic Council

After the pirate’s assault on Auridon Ju-Lihen will ask for your help in rescuing her sister. Go with her and uncover a strange artifact. Upon your return the master of Auridon will ask you to collect more artifacts.
This will wake the Synod’s interest in Psijic’s affairs, leading to an unpleasant altercation in Winterhold. For all your assistance the Psijic Council will offer you a seat at the table.
Complete a class at Auridon Academy and undertake the Psijic Trials and you will earn your Circlet of the Council.

Meeting the Synods

After being taken prisoner by the Synods you once more gather up the Psijic Council, who decide to deal with the rising threat of this magical authority.
In your efforts to stop the oppression of magic you learn about the real reason the Synods and pirates have been assaulting the Psijics.
Find out more about the conspiracies that are besetting the council and travel to the Synod headquarters and deal with the mages.

Sailing for Summerset

With the Synod threat neutralized it’s now time to deal with the root cause of the Psijic troubles.
Together with Ju-Lihen you will be asked to travel to Summerset and learn more about the Thalmor party and the mysterious Lord Priests who are in charge of it.
Travel to Summerset and discover a whole new land with strange creatures, magnificent cities, haunted forests and legendary ruins.

Rebellion at Summerset

When reaching Summerset Ju-Lihen will introduce you to her old friend Arbalyn. Together with a group of men Arbalyn is planning to revolt against the capital of Alinor, and the Lord Priests that hide within. Help him and his soldiers build up their army, liberate cities and kill the Thalmor so that they may challenge Lord Priest Smulder’s rule over Summerset.

Completing the Psijic Council

In your endeavours to overthrow the Thalmor you will eventually hear of the Psijic members who chose to remain on Summerset when Auridon and Artaeum was separated. Free the Artist from the pirate’s clutches and he will tell you where to find the last Pillars.
One of the Council’s oldest living members, Glenadir, will help you identify a relic, given by a Thalmor defector. But before you can use it, it has to be infused with enourmous amounts of power.
Gather the Psijic Council with the Pillars of Summerset joining the circle.

Charging the Staff of Towers

Learning about the Staff of Towers you find that it cannot be charged using normal Soul gems. Instead you need to find and bring a familiar artifact to the Crystal Tower, at Summerset. Bring the Eye of Magnus to Summerset, and charge up the staff.
With the rebels winning more ground a handful of Pillars decide to join you on Summerset. Bring them into KArndar Desert to test the powers of the staff.

Fighting with the rebels

After learning about the Staff of Towers magical properties you should try to find how it can be used in the civil war of Summerset. Arbalyn and Rusten have different ideas on how to proceed, and will look to you for answers.
Advise the rebel leaders and choose which battlestrategy you think will be the best, in order to finally surround the Thalmor capital.

Learning about the Thalmor weapon

With most of Summerset now under rebel control the rebel spies have uncovered that the Thalmor have some secret weapon that they’re hiding inside the Alinor Spire, guraded by the Lord Priests themselves. Use the rebels’ growing network of supporters to find out what the weapon is and where it came from.

Conquering Summerset

After losing Ghille in the past you and Ofelia have to fight your way back through a mysterious realm of ghosts and daedras.
Upon your return Karolin will inform you that the assault on Alinor has begun. Conquer the capital of Summerset and challenge the Lord Priest, who calls himself Smulder.

Kick back and have a drink

After the Thalmor have been defeated Rusten goes to enjoy a cold drink at the capital’s pub. Join him there to learn what will happen to Summerset, before returning to your own adventures.

The image above shows the EditorID of all the quests you go through, to complete the main story. (High-res version)
Green means it has the prefix ARTAEUM
Blue means it has the prefix AURIDON
Red means it has the prefix SUMMERSET