CASTLE - "Deep in Death" -- When the new season begins, Castle (Nathan Fillion) is wrestling with how to repair his relationship with Beckett (Stana Katic), while struggling to finish his soon-to-be-published bestseller, Heat Wave. But circumstances force the pair back together to investigate the mysterious murder of a man found dead, tangled in the limbs of a tree. The Season Two premiere of "Castle" airs MONDAY, SEPTEMBER 21 (10:01-11:00 p.m. ET) on ABC. Authors Stephen J. Cannell and Michael Connelly guest star as themselves in the episode. (ABC/MICHAEL DESMOND) ELIZABETH HO, STANA KATIC