Five main cast members–Sibylla Budd, Spencer McLaren, Dan Spielman, Nina Liu, and Gigi Edgley–left at the end of season three and original lead Samuel Johnson left early in season four, followed by Michael Dorman three episodes later. Original cast members Deborah Mailman and David Tredinnick continued, and seven new regular characters were added for season four. The changes were part of a larger overhaul which had the arrival of a new producer, a new script producer, and a new writing team.