Everything will be set in motion by a bad egg
Firstly, I think that we're on the cusp of finding out that Pete is a horrible guy. In the comic series Rick makes note of a few untrustworthy things that Pete does and comes to the conclusion that he's abusing his family. Rick is unable to control himself and instead attacks Pete, engaging in a huge fight which ends with Douglas (the comic version of Deanna) intervening. Douglas resists Rick's request to exile him because Pete is a doctor and useful to the community, instead he is made to move into a new house, away from his family.
A new group of baddies is introduced
Meanwhile, while out on a supply run, the runners get trapped by a a surprise herd of walkers. They eventually find out the herd was caused by a group of scavengers, led by a guy named Derek. The scavengers have been trapped in a building by the walkers for a week, and eventually they forced one of their own group out into the street to be eaten by the walkers, and allowing them to escape. I think that it is this group that will be the mysterious Wolves that we have been seeing hints of since the mid-season premier. As the runners from Alexandria leave, Derek and his group hear their vehicles and pursue them.
The troubles in Alexandria continue
Meanwhile back in Alexandria, Pete has become so enraged with how he was treated that he confronts Rick with a knife, and when Douglas's wife, Regina (the female version of Deanna's husband Reg) tries to intervene she is slashed and killed.
As a result of a completely innocent party being killed (Regina), Douglas realizes that it's too dangerous for Pete to be allowed to stay and tells Rick to shoot him.
The final showdown
With the sound of Rick's gunshot ringing in the air, Derek and his group head in the direction of Alexandria.
Derek then confronts Rick at the gate, and greets him with a rather famous phrase, and one which makes me think that this has to be the reason that Derek's Scavenger group from the comics will be the Wolves in the TV show:
Come on! They have to be the Wolves, right?!
However, just like in the fairy tale, the big bad wolf never triumphs, and thanks to some sharp shooting by the newly instated lookout (Andrea in the comics, Sasha in the TV series), Derek and his cronies are swiftly dealt with, after all Rick and co have had tougher challenges than these guys.
With Pete and Derek's group taken care of, the finale will end with Deanna, in much the same way as Douglas, handing over leadership to Rick after realizing that he and the group can make more informed choices for Alexandria due to their experience living outside of the walls, hence the title of the finale being "Conquer."
With the Ricktatorship reinstated, the only loose end for Season 5 will be Morgan, who I'm betting will appear at the gates shortly after the Wolves are annihilated, providing brief panic before he removes his mask and Rick realizes it's his old friend.