My wife Heather and I are both avid listeners of “Serial,” the public radio podcast that reinvestigates a 1999 murder in Woodlawn, Maryland — just a few miles from Baltimore, where, as it happens, we live. A couple of weeks ago Heather had to take a medical licensing exam at an office park in Woodlawn itself, and as we drove out we realized we were passing through the show’s geography. Our car suddenly became very grave.