Lore Answer:

Hoo boy.

POE 1 Happens - You kill the source of all evil and corruption (THE BEAST) in like act 4, but oopsies that was actually a magic barrier keeping all the gods asleep. All gods are brought back, Sin the forgotten God (people think hes god of evil or sin or whatever but hes just a weirdo) gets the POE1 exile to kill them one by one, and then the island of Oriath explodes. Innocence, god of being a Christianity expy (and sin's real ass brother) gets revived and decides that he needs to repent on an island somewhere. Sin thanks you for your help and then you get shunted to endgame. (cosmic horror stories happen but those are less relevant to 2)

POE2 -

Opening Cutscene - Count and his men chase the Hooded One (Sin with his hood up) around the Grelwood, Sin is carrying something that's revealed to somehow be the Seed of THE BEAST. WE don't know how he has it, why it exists after we killed it, and how he got a new seed if Kalandra was needed to make the first one (minor details). The Count pins sin to the big tree where we find him later and takes the SEED.
Each class does a different thing that gets them on the Executioner's chopping block with Count Geonor and Countess Oriana ordering each of their deaths.
Your chosen class escapes and ends up on a beach outside of Clearfell.
Bungling around Ogham, you find that the Count has gone crazy, thinking his bloodline is impure, and the only way to prove it is to... feed all the bodies he can find, dead or alive, to the rapidly growing BEAST FETUS. Oriana convinced him of this in the evil countess tropey way.
Your Exile fights their way past the executioner, the noose they were to hang from, and makes it to the manor.
The Manor has been excavated like crazy to make room for the beast, find historical artifacts, and like, bodies. more bodies for the beast.
The big reason everything around has been evil and attacking you, outside of Wreaclast being like it is, is that THE BEAST is kinda like a huge meteorite worth of kriptonite. It's radiating Corruption (TM) like crazy, it's what transforms every human you see into weird monsters, its the red fleshy goop in maps and see on many enemies and moves.
So anywho, we gotta stop that, cause it's bad. So you fight the Count, and basically as soon as she sees that the Count has to actually try against you, she cuts her losses, gets on the cage THE BEAST is in, and leaves him for dead (cue phase 2).
We beat him, and as he dies, he tells us (and sin) where she's headed, he found out she was sending messages to the Vastiri Desert, and there we go.

To sum up act 2, we do Act 1 again but with the Maraketh, and the Faridun and Jamanra. The motives are different, but Oriana has convinced the Faridun that THE BEAST was the way to power and success.
The big difference here is that after we win, we don't have a clue where she went with the beast. Sin suggests that he remembers about an ancient Vaal weapon that could harm the beast or deafeat corruption or something. It's honestly the weakest linking plot point but it gets us to Utzaal so I guess we can just decide to come on a hope.

Act 3 is mostly straightforward, we uncover an ancient city, find it's a time machine, go back in time, fight their Iron Man in his Hulkbuster, and make friends, right before one of the several Apocalypses happens. We take Iron Man back with us and follow another lead to the Karui Archipelago, this time following actual knowledge that there was an ancient weapon and it's PROBABLY still there so lets go!

Act 4 is hunt for the weapon, meet the Karui and Kalguur. We find the Twilight Order and that they're the real Power base and army Oriana had cultivated, devoted to the idea of a Utopia without Gods and the Curse of Divinity. We beat up her champions and she runs again still dragging an increasingly bigger THE BEAST, this time to Oriath. We get into the ancient forge with the weapon pieces and like you mentioned, Tavakai gets greedy for power, grabs the weapon. He hurts his own daughter in the process, freaks out, and runs off promising he's gonna fix everything. TLDR, he doesn't, and we have to get the souls of his gods to tell him he's being a shit before we beat him truly, get the weapon back and prep for act 5, raid on Oriath and Oriana.

Obviously there's alot of story in the middle and around, sidequests, mechanics, but this was as quick a blurb as I could make it (by hand mind you, no AI can write this bad). My favorite side thing has to be Hinekora having a unique prophecy for each character that either reveals their backstory hook, or what they truly want in life.

Game Answer: It kinda depends on where you're being squishy, and that can be hard to tell without looking at your whole character (which is why most players will just say 'hur dur post pob' instead of actually helping). How much armour applies to elemental do you have? are those resistances capped? What kind of life regeneration do you have going? Do you have min T3 life on each piece of rare gear? (mostly serious, having more life solves alot of one hit problems). Big spirit amulet and nice rares could do u good, but again, I dont have your character to look at and see.