This mission is one of the more difficult in the game, since there is almost always extra text from keeps or allies taking too much damage. A lot of time is spent taking down captains to avoid these messages, but there is not enough time to clear everything.
Head to West Sanctum. The Dinolfos in front of it should aggro as you pass by.
Take West Sanctum, killing the Dinolfos in the process.
The Dinolfos in front on West Sanctum follows you around the whole map until you kill it.
Stay inside West Sanctum until the "You discovered West Sanctum!" message appears.
Head to and take South Sanctum, then East Sanctum.
Kill the Dinolfos south of East Sanctum.
Kill the Poe northwest of Zelda.
Take the outpost North of Fairy Fountain.
Kill the Dinolfos by that outpost.
Kill the Poe in Western Keep.
Try to avoid taking Western and Eastern Keeps, since if they go in peril, you will get extra text.
Kill the two Dinolfos north of Fairy Fountain.
Clear as much as you can between Zelda and Fairy Fountain.
Load Zelda for as much of the escort as you can, making sure to clear anything that she aggros on.
You want Zelda to reach the Fairy Fountain before the "Midna is advancing toward the Fairy Fountain!" message ends.
Check Midna's health and location. If she's low on health and in West Ruins, clear the Dinolfos and Poe off of her.
Go clear for Western Keep some more while waiting for the magic circle to appear.
It appears on the "Help Zelda activate the magic circle!" message.
Activate the magic circle.
Head to Eastern Keep, clearing enemies around Darunia.
Be sure not to kill the highlighted Poe.
Use the boomerang on the highlighted Poe to stun it, then run into it to push it as far north from Darunia as you can.
If the Poe is too close to Darunia, he will give you extra text.
Once "Mission Failed" appears and the Poe isn't highlighted anymore, kill the Poe.
Head to East Ruins Room.
Once the gate opens, kill Volga without taking the keep.
Kill the Poe in front of the keep Cia is in, taking the magic pot.
Healthgate Cia once the gate opens.
The way to kill the Cia clones quickly is to activate magic at the right time so that the explosion when time runs out hits all four of them.
If there are no extra messages that play, activating magic about halfway through Cia's "Do you really think you can defeat me? Mwa ha ha! Why don't you disappear!" message works well.
Extra messages can include ally in trouble text. These will make the Cia's take longer to appear. If you are expecting one to appear, it might be a good idea to wait to activate magic later.
If Lana is already dead at this point, there will be one less message before the clones appear. This would mean you want to activate magic one message early assuming you don't get any other extra text.
When the Cias first appear, the healthgate on the original Cia is still active. If magic explodes too early, that Cia could survive.
Take damage while waiting for magic to expire. Drinking a potion right before the time runs out will extend the magic while drinking, potentially stalling long enough to spawn the clones or wait out the healthgate.