Right, so thing literally go tits up right from the menu screen. Following events of Dragon Age 2 (which concluded with Anders blowing up the Chantry, inciting Mages to rebel against the way they're controlled) the Divine has organised a last ditch effort to broker peace, gathering the respective leaders in the Temple of Sacred Ashes. The minute you press the start (alright, the options button) the Temple blows up, a huge green explosion wiping out everyone within half a mile.
Your character drops into the fade, whereby you get to customise them, choosing race, gender etc. I'm a mage again, obviously. Typically mages are really strong late-game in Bioware games, so that's how I usually roll my first play through. Anyway, you crawl towards a glowing yellow figure on a hill, extending your hand at which point it glows with green fire, and you then fall out of the rift into the crater left by the explosion. You awaken in chains, being questioned By Cassandra, who you may remember from DA2. She believes you to be the cause of what they call The Breach, a hole in the sky following the explosion that is allowing demons to pour through it into our world. To make a point, she takes you outside and shows you it. It pulses with green light, and the green fire on your hand does the same. Cassandra explains The Breach is causing small rifts to appear as well, which are also spawning demons, and asks how you did it. Still protesting your innocence, Cassandra drags you along to investigate The Breach. Along the way, a stone bridge you're on collapses, and you're both plunged onto a frozen river whereby demons attack. Cassandra fights one, but another closes in on you. You pick up a weapon that just happened to be laying on an overturned cart nearby and fight the demons off.
Fighting your way to a small rift nearby, you defeat the demons there and an elven mage grabs your hand, pulsing in response to the rift, and thrusts it forward, closing the rift. Would this then work on the Breach? Why not? The elven mage is Solas, an apostate mage who happens to be an expert on the Fade, and with him is Varric, the story telling dwarf narrator of DA2. He and Cassandra don't really get along. Shortly after, you find your way to a bridge where Leliana is arguing with a random Chantry Cleric. Cassandra quickly reminds him he has no authority, and ignores his requests to arrest and execute the player character.
The Breach is just up ahead, but there's a problem. It's heavily defended, and while some scouts did try to come at it from a different direction, by taking the nearby mountain pass, they've not been heard from. At this juncture, you're faced with a choice; go with the soldiers and attack head-on, or follow the scouts through the mountain? Being a mage, I opted not to go blindly rushing in, and crept through the mountains. Upon exiting the other side, you find what's left of the scouts being attacked by demons coming from another rift. You beat the demons and close the rift, sending the scouts back to safety whilst you advance to The Breach.
The Breach, hanging over the smoking crater that was the Temple, looks unguarded, and the fade is weak here. Cassandra sees an echo of the Divine being attacked by a figure obscured from view, and she calls out for help, only for the player character to appear seconds before the blast that destroyed the temple, unable to help. Your innocence proven, to Cassandra at least, Solas informs you that the rift beneath the Breach is actually dormant; still active technically, but it will need to be opened before it can be closed properly. You use you glowing fire hand - referred to as "the mark" - to open the portal again, prompting an enormous Pride Demon to come through and start stomping you. He's actually really quite challenging for this point in the game, but by interacting with the rift itself, you can stun him and weaken him for a few seconds which lets you hit him much harder than normal. In this manner, he's taken down, and the Rift is closed, though doing so takes a toll on your character, the sheer force of closing it sending out a shock wave that reaches all the way up to The Breach and knocks you down, clearly out of action for a while.
You wake up in unfamilar surroundings, a rather nervous elf girl seeming in awe of you, and insisting she must tell Cassandra you're awake. You stroll through the ranks of amassed, and head on into a Chantry building where you interrupt Cassandra, Leliana and the earlier random Chantry Cleric, who Cassandra addresses as Chancellor Roddrick. He again insists you are executed, and again Cassandra ignores him, this time they argue a little longer until Cassandra pulls out a big thick book and tells him that she's reforming the Inquisition of old.
Finally, an hour into the game, you get a title screen!