In the G-S Defenders story, Clea tells Valkyrie stories of her teammates' past battles; however, she unknowingly invokes a spell that causes Dr. Strange, Sub-Mariner, and  Hulk to relive those battles. The old battles are reprinted material by Kirby, Everett, and Ditko, the new sequence with the three fighting their old menaces is new by Starlin.

I have to say I'm surprised by the choice of Defenders #13 for the cover. I'd have thought any volume including G-S Defenders #1 would use that for the cover.

So let the speculation begin for Defenders Masterworks Vol. 3! I'm guessing Defenders #'s 17-20, G-S Defenders #'s 2-4, Marvel Team-Up #27, and Marvel Two-In-One #'s 6-7.