Related Clues:

• Where to begin
• First stage
• Get to work
• Crank up
• Word on a maze
• Take step one
• Maze entrance word
• "Boo!" reaction
• First square of some board games
• Sudden movement
• Be part of the opening lineup
• Word next to an arrow, maybe
• Possible result of a gunshot
• Boot up
• With 21-Across, begin from scratch