The first season of “Only Murders in the Building” was a treat for this jaded viewer, a potent, intelligent mix of tight scripting and witty improvisation from Steve Martin and Martin Short, so Season 2 faced a high hurdle. The amateur podcasters (the two stars plus magnetic Selena Gomez), fresh from solving a tricksy Season 1 crime in their Arconia apartments in Manhattan, find themselves under suspicion for an especially baffling, locked-room murder puzzle. Weaving in a nifty set of subplots, some of them harking back to the earlier show, the plot bucks and weaves over the first few episodes, and in the early second half, I found myself almost nonplussed by the complexity (which is, of course, part of the point of this true-crime mash-up). But the final two of the ten episodes are triumphant, zipping together all the many threads with such brilliant, ramshackle humor that I almost fell out of my seat gasping and laughing. Now that the follow-up season has eclipsed the debut show, what can we expect from Season 3 of Only Murders in the Building?