 The third season was initially planned to include three separate mysteries that would be introduced and resolved in a series of non-overlapping story arcs. Thomas realized by talking to CW Entertainment President Dawn Ostroff that viewers got too confused by his original format, and the new format would allow new viewers to start watching at any point in the season. Inspired by the improvised thriller Bubble, Thomas started laying "subtle" motives for the second mystery during the first one, so that fans would have "a theory on whodunit" when it occurred. The first mystery took place over the first nine episodes. Originally, the second mystery was to be seven episodes long and the third mystery was to occur over the last six episodes of the season. This was changed when The CW ordered a 20 episode season instead of the usual 22 episodes. The second mystery arc was shortened from seven episodes to six, and the third mystery was first changed from a six episode arc to a five episode arc. After an eight-week hiatus for the series was announced, the final mystery was changed to five stand-alone episodes designed to be friendlier to new viewers. The final mystery was originally going to be "unlike any of the others we 've done before". Previously, "nice characters" like Wallace and Mac had always been absent from the big mystery because no one was going to believe them as a suspect. For the third mystery, Thomas had wanted to present a situation where Wallace and Mac could be fully involved, "key players [with] really interesting stuff to do".
