Log in to get free access to the next mini-mission or pay later.
This is why I have no desire to try returning to GW2. There's too much content that I missed by not logging in at the right time, and coming back in the middle or end of whatever they're doing now is unappealing.
I wonder if their model actually makes more money than flipping it around--make each episode pay for a few weeks or months (depending on how fast they release stuff) and then free afterward. Pretty much every other larger MMO has done this, if nothing else than by bundling past expansions with later ones so it's easier (and cheaper) to get back into things.