Possible Clues:

• Thus commences crude work
• Work offered to single trainee
• Break one's back, but not really
• ''. . . ___ and trouble'' (''Macbeth'')
• Trouble partner, in Shakespeare
• "Bubble, bubble, __ and trouble ..."
• Work wearyingly
• "Double, double ___ and trouble ..."
• ''Double, double ___ and trouble . . .''
• ''Macbeth'' witches' word