Merlin (8pm, NBC) - NBC didn't score with their futuristic retelling of David & Goliath, but maybe there's magic in "Merlin," a fantasy show about the pre-Camelot years of Arthur. Stars Anthony Head (left), who played Giles on "Buffy the Vampire Slayer." Back-to-back episodes at 8 and 9.
Impact (9pm, ABC) - Part one of a two-part sci-fi movie about the moon on a collision course with the earth. Starring James Cromwell and Steven Culp.
True Blood (9pm, HBO) - Sookie goes too far in helping Jessica adjust to her new life, and Jason makes an enemy at the Light of Day leadership conference.
In Plain Sight (10pm, USA) - Mary's sister Brandi is charged with drug trafficking and murder.