Related Clues:

• With 21-Across, begin from scratch
• Outset
• Machine button
• Turn a key, perhaps
• Word next to an arrow in a maze
• One end of a maze
• "___ the Revolution Without Me" (1970)
• Zero hour
• Involuntary jerk
• Step one
• Jump into
• False __
• 'Go' square in Monopoly, e.g.
• Begin work on
• Jump suddenly