In June, it seemed as if any day might bring about the collapse of the Greek economy and with it, the entire euro zone and its decade-old currency. Then in July and August, it seemed as if everyone was on vacation. Now they’re back — finance officials and political leaders have been flying all over Europe to meet with one another — and along with them the crisis that has been raging for the last two years. Here is a guide to the new season’s most intriguing (and terrifying) story lines.