Jojen Reed is credited in every episode, along with Beric, Mance, and Tormund. That might be contractual, or they might just be in every episode.
Ep. 301 – Valar Dohaeris - Is a lot of action to catch everyone up, and to establish new story lines:
Introduction to the BwB w/Arya & co, action at The Fist, Dany & Co leave Qarth/arrive Astapor (and meet Missandei & Daario- who is just a little übersexy), we meet The Reeds, Queen of Thorne's arrival in KL (if I hired Diana Rigg, she'd be in every episode), Mance & Co/Jon, The Tullys, Theon & RAMSEY, Karstark, Shireen & the new Selyse, Davos stranded, Jamie & Brienne - Jamie loses his hand at the end of the episode. *WHEW*
Ep. 302 – Dark Wings, Dark Words
Robb and Cat hear about Bran and Rickon. The only cast listed so far are Jojen, Beric, Mance, & Tormund. I think we have the arrival of Sam's Ravens as well. Davos rescued/imprisoned. News the Freys are a little angry.
Ep. 303 – Walk of Punishment
Theon in the hands of Ramsey. Fist survivors walking to the wall. Slayer? The same cast from Ep2 is listed, but we also meet Martyn Lannister. Davos pardoned.
Ep. 304 – And Now His Watch is Ended
Mutiny at Craster's Keep and Joer's death, Hoster death and funeral, Balon's death (Asha/Yara is in the trailer, so why not set up the Queens/Kingsmoots? We meet Wendel Manderly and the Great Frey Apology begins. Davos learns to read.
Ep. 305 – Kissed by Fire
Sexy time with Jon and Ygritte, the duel between Beric and the Hound, Beric's ressurection, and Dracarys for the slavers.
Ep. 306 – to be determined - Scaling The Wall. We meet a tortured slave.... who is credited in IMDB. Nice place to continue the Iron storyline not necessarily the new Greyjoys but Asha & The Reader, and introduce Oberyn, Ellaria, and the Kettleblacks in KL.
Ep. 307 – The Bear and the Maiden Fair
Bran has a REALLY bad dream. Bear Pit scene w/Steelshanks, definitely something between Jorah and Dany, definitely Tyrion and Sansa's wedding. Back in the Vale w/Lysa & Robin (because IMDB says so.)
Ep. 308 – to be determined
Dany arrives at Yunkai and meets Mero, Jamie and Brienne continue journey to KL. Queenscrown. THE RED WEDDING. (Rains of Castamere is the GO signal.)
Ep. 309 – The Rains of Castamere
Arya's thoughts about RW. Bran & Co heading north. Jon heading to Castle Black (faster.) Joffrey's Wedding prep (where he says he wants Rains of Castamere to be played almost nonstop....)
Ep. 310 – Mhysa
Obviously Dany. Joffrey Wedding. Arya has Nymeria dream and pulls cat out of he river, but men are coming..... It's Beric & Thoros, who find Cat... Joffrey gets drunk. Jon arrives at The Wall. Davos tells Stannis about the message from The Wall. Joffrey dies, Cersei calls for Tyrion's arrest. Beric dies as Lady Stoneheart opens her eyes.