Related Clues:

• Possible result of a gunshot
• Boot up
• 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)
• Signs of fright
• Zero hour
• Involuntary jerk
• Step one
• Proctor's instruction
• Jump into