MIDSEASON FINALE: This is what the networks, cable and broadcast, increasingly are calling their final first-run episodes of the year before the holiday break. I suppose it’s because “midseason finale” sounds a lot better than “the last episode before we pack things up until the New Year, when people start watching TV in large numbers again.” But on this particular midseason finale, we’re supposed to solve the murder that was introduced way back in the series premiere. My money’s on Professor Plum, in the library, with a lead pipe.