I can't wait for episode 5 and I spent a lot of time analyzing stuff trying to figure out what will happen next, and here are my predictions.
So the episode will begin with a massive horde of walkers entering Savannah. You learn that Clementine is being kept in Crawford at the Marsh House, where her parents were staying. Lee and the group will head there (or just Lee, depending on what happened at the end of 4), and on the way you will run into Molly.
Molly does NOT die in episode 4 no matter what you do. Even if you accidentally shoot her, if you look carefully, you see her run away and the walkers chase after Lee and Ben.
However, if you / Clem helped Molly in episode 4, she will help you reach Clementine. If you shot her / left her, she will not help you. It is harder if you don't have help because Lee begins to turn and get very weak.
Lee will reach the Marsh House where Clementine will be with the walkietalkie man. Clementine's mom is there along with a few other survivors, and she is very ill. We learn Clementine's dad was bit and killed, but Clementine's mom survived hoping to return home. Walkie talkie man doesn't want Lee to take Clem, because he thinks she is safer with him. He is about to kill Lee (if you have Ben with you, Ben is shot and killed) and suddenly Clem's mom turns and attacks walkie talkie man. You have the choice to either kill Clem's mom, or give Clementine the gun and have her do it. This decision is very important to the ending.
You make it back, and it will be Kenny, Christa, Omid, Lee, and Clementine no matter what.
They get on the boat JUST as walkers are right behind them.
They start to go towards one of the islands (there are many small islands surrounding Savannah) when Lee gets very sick and starts to cough up blood.
If you told the group about the bite, they will help you. If you didn't tell them about it, they will see it now and they will hate you for putting their life at risk.
The boat will have problems at this point and Kenny will realize that they can't make it to the island with all these people, and someone needs to jump off. If you hid the bite, Kenny will want to throw you off because you are dead anyways. Christa and Omid stay neutral but Kenny will want to throw Lee off, when suddenly Kenny is shot in the stomach and falls into the water, and we see Clementine is the one who shot him.
This explains why the voiceactor who plays Kenny says he doesnt know if Clem lives or dies, because Kenny will die before the ending so he doesn't know what happens after that.
They make it to the island where there are VERY few walkers and they realize there is a lot of food/supplies here.
Lee will begin to die at this point, he will be unable to move, and him and Clem say bye in a very emotional scene while Christa and Omid watch. Then Lee gives Clem the gun and tells her to end this.
NOW, this is when EVERY single decision you made from episode 1 will come into play.
[*]Killed the St. John Brothers
[*] Killed Larry
[*]Stole from the car
[*]Left Lilly on the road
[*]Gun-trained Clem properly
[*]Brought Clem to Crawford
[*]Let Clem shoot her mom
Clem will SHOOT Lee, showing she has become a survivor and will do whatever it takes to survive, as she learned from Lee. If you DIDN'T do major things, like letting the St. John brothers live, bringing Lilly with you, and not killing Larry, Clem will hesitate in shooting Lee and Lee will turn and jump on Clementine and Christa/Omid will shoot him off.
The game will end with Clem being taken care of by Christa/Omid. Every character has had some sort of purpose except Christa/Omid, but as a couple, they will be able to provide Clem with stability and they are strong survivors too.