401: Two Swords
Official synopsis: Tyrion welcomes a guest to King's Landing. At Castle Black, Jon Snow finds himself unwelcome. Dany is pointed to Meereen, the mother of all slave cities. Arya runs into an old friend.

Tywin forges Oathkeeper. Tyrion welcomes Oberyn Martell to the city (who promptly stabs a Lannister guardsman). Jon Snow faces opposition from those who think he is a traitor. Dany marches on Meereen and finds the bodies nailed to trees pointing the way. Arya recovers Needle.

402: The Lion and the Rose
Official synopsis: Tyrion lends Jaime a hand. Joffrey and Margaery host a breakfast. At Dragonstone, Stannis loses patience with Davos. Ramsay finds a purpose for his pet. North of the Wall, Bran sees where they must go.

Tyrion gives Jaime his golden hand. Joffrey and Margaery's wedding, Joffrey's death and Tyrion's arrest. Stannis and Davos debate on what to do next; either they decide to head for the Wall, or Stannis decides they will visit Braavos first to win the allegiance of the Iron Bank. Ramsay finds a mission for Theon, either trying to track the Stark boys or going to force the surrender of Moat Cailin. Bran gets directions to the Three-Eyed Crow via weirwood (Coldhands has not been cast this season).

403: Breaker of Chains
Official synopsis: Tyrion ponders his options. Tywin extends an olive branch. Sam realizes Castle Black isn’t safe, and Jon proposes a bold plan. The Hound teaches Arya the way things are. Dany chooses her champion.

Tyrion is imprisoned and ponders how to defend himself. Tywin's olive branch is either to Cersei or Jaime, but is likely rebuffed. I can't remember if Jaime gets Oathkeeper in Episode 1; if not, it makes more sense for him to get it here. Jon's plan is likely his 'punishment raid' on Craster's Keep to wipe out Rast and the other traitors. Dany chooses Daario to defeat the champion of Meereen, which they are besieging.

404: Oathkeeper
Official synopsis (last one available): Dany balances justice and mercy. Jaime tasks Brienne with his honor. Jon secures volunteers while Bran, Jojen, Meera and Hodor stumble on shelter.

Daenerys chooses what to do about Meereen, and may even take the city before the episode is over. Jaime gives Oathkeeper to Brienne and dispatches her to find Arya. Jon raises a posse for his Craster's Keep mission. Team Bran either find the Three-Eyed Crow or inadvertently stumble on Craster's Keep themselves.

405: First of His Name
Tommen is likely crowned and Daenerys may choose to stay in Meereen (as both would be the 'first of their names'. It is possible that Balon (also the 'first of his name' as a claimant) dies in this episode, and Stannis may visit Braavos and win the support of the Iron Bank (they might acknowledge his legitimacy to the Iron Throne by saying he is the first of his name). It's also been suggested that the Iron Bank sends a Faceless Man (Jaqen?) to kill Balon after agreeing to support Stannis.

406: The Laws of God and Men
Tyrion's trial is likely well underway by this point.

407: Mockingbird
Either 1) Littlefinger helps Sansa escape (she doesn't escape when she does in the book, as she's present at Tyrion's trial) or 2) Sansa escaped an episode or so earlier and arrives in the Vale this ep. We possibly even get Lysa and Petyr's marriage in this episode.

408: unknown
Possibly the Oberyn/Gregor duel. Maybe Arya getting on the boat to the Free Cities.

409: unknown
The big battle episode featuring Mance Rayder's assault on the Wall and his defeat at the hands of Stannis Baratheon. The majority of the episode or even all of it might be focused on this one location.

410: unknown
Big season finale. Likely Tywin's death, Tyrion's escape and Jon's election as Lord Commander. Possibly Lysa's death as well. Final shot: either Arya seeing the (already-established) Titan of Braavos appearing on the horizon, or UnCat revealing herself (possibly to Brienne rather than as in ASoS).

Things that will happen, but we just don't know exactly when:

Ygritte and Tormund's raiders attacking villages near the Wall. Their attack on Castle Black, although some rumours say their raid from the south happens simultaneously with Mance's attack from the north in Episode 409 (which makes a lot more sense than in the book).

Team Bran run into the Night's Watch traitors at Craster's Keep. It's unclear if this is a narrow miss or they are captured. It is known that Jon attacks and wipes them out, and presumably Team Bran escape before this. A Jon/Bran meeting seems unlikely. Team Bran reach the cave of the Three-Eyed Crow before the end of the season, but when is unknown.

Daenerys takes Meereen, resolves to stay and do justice and is presented with the bones of the child Drogon eats. Daenerys meets Hizdahr, but does not appear to have decided to marry him yet. More intriguingly, Ser Jorah is still with her when the bones of the child are presented. It is possible that the discovery of Jorah's betrayal is delayed to provide a cliffhanger where Dany's storyline doesn't really have one (since it seems to go at least a little way into ADWD before concluding).

Stannis and Davos visit Braavos and win the support of the Iron Bank; this is an ADWD storyline, but done in Braavos rather than in the snows outside Winterfell, and before the attack on the wildlings rather than afterwards.

Brienne's storyline is up in the air. It may be she only completes part of her AFFC storyline, or it is cut down and she does all of it and is hanged by UnCat in the final episode.