Dalton captures you after you awaken on the ruins of Zeal.
Escape the Jail
When you awaken, all your stuff (equipment, items, gold) is gone. You don't have to get it back, but it makes things easier. If you don't get your gold back now, you lose it forever.
From your cell, go up the ladder. Then go back down and someone will notice an air duct. Go on up it.
From the spot of light, go right, up, left, straight, up, up, left, up, and down the ladder. Don't touch the guard, and open the chest, then go back up the ladder.
From here go down, right, down, down, right, right, down, left, straight, up, and right and down the ladder. Fight the guards to your right (if a Byte floats onscreen, wait for it to go offscreen again before fighting the guards). Then go in the room, defeat the Byte, and open the chest. Go back out.
There is a conveyor belt to the left, go down it. Then, go in the door to your left. Beat the guards to get your gold.
Then go back out, switch the conveyor belt below to go down, and go down that. From there, go left and through the door. Beat the guards and get the chest. Go up the ladder.
Follow the path, and when you get to the first spot of light, go up, right, straight, up, left, straight, up, up, up, left, and down the ladder. From here, go down the left path, then switch the conveyor belt to go down, and go down it while the Byte is offscreen. Go through the door here, beat the guards to get your items.
Now, you CAN go through the door in this room, but there's a Magic Tab waiting for you in the ducts now that you've gotten everything back. So, leave the room the way you came in, switch and go up that conveyor belt, up the top left path, then up the ladder. From the ladder go right, right, and when you hit the wall, down and around to where the Tab is to get it. Then go back down the ladder you came up from, down the left path, switch the conveyor belt to go down, and go through the door here.
Inside, go through the door at the top, then up the ladder.
The Turrets on the wing are like Rubbles, they give lots of experience and tech points, but might run away during the battle. You can just ignore them. Head left.
When you're all the way to the left, let yourself get blown back to the bottom of the wing. Here comes a boss...
You don't have to beat this guy, he doesn't attack, and eventually he runs away. The experience is good though, so hit it with Beast Toss until it dies. Make sure to have Frog use a Mid Ether on Robo as necessary.
Pretty easy. Just hit with physical attacks until he's gone.
Back on Epoch, when you're prompted, hit Y, then X.
After you land, check out the Nu for new stuff.
Now go to the top of North Cape and check the sparkle and Magus appears. After he mouths off on Crono, the group (or Frog alone if he's with you) decides to fight him.
It's up to you if you want to fight. If you don't fight Magus, he'll join you! If you do fight him and beat him, he's dead and gone forever, and all you get is his Amulet. If you want him, say you don't want to fight, then as you leave, Magus joins (default: Magus).
No matter what you do, Magus tells you something interesting about Crono's... situation.