In this episode, three epic battles: Jane Mayer recounts her experience investigating—and being investigated by—Koch Industries; Junot Díaz discusses his fraught relationship with his native Dominican Republic; and the undefeated boxer Heather Hardy prepares for a big fight at the Barclays Center. Finally, the astronomer who wrote “How I Killed Pluto and Why It Had It Coming” lays out his evidence for the existence of a ninth planet.