Good Grief! Charles Schulz’s biographer reveals some surprising secrets about the creator of “Peanuts.” And we hear from a mother and daughter who learned about the US from the comic strip, living in Panama. We’ll visit Berlin with Detroit-born poet Sadiq Bey and our special correspondent Fiona Chutney. Plus, Led Zeppelin rock god Robert Plant joins forces with bluegrass star Alison Krauss for an album of twangy covers.