24: Season 1
Such a simple idea--yet so fiendishly complex in the execution. 24, as surely everyone knows by now, is a thriller that takes places over 24 hours, midnight to midnight, in 24 one-hour episodes (well, 45-minute episodes if you subtract the commercials). Everything takes place in real time, which means no flashbacks, no flash-forwards, no handy time-dissolves. Every strand of the plot has to be dovetailed and interlocked so things happen just when they should, in the right amount of time. Not that easy.
