Now, that’s what I call a flashback! One week after I complained that Silo had denied us the full Salvador Quinn backstory I wanted, this week’s episode begins with a much more recent flashback, putting all of Juliette’s adventures in Silo 17 into a surprising new context. Add in one whopper of a closing cliffhanger in Silo 18, and “The Safeguard” delivers all the tension and plot development missing from “The Book of Quinn.” If this episode were a chapter in a book, it’d...