Possible Clues:

• Directionless man goes about desert
• Capricious boy about to betray one's trust
• Water rat I consider to some extent unpredictable
• Variable payment for killing trapped vermin
• Volatile
• Heather almost trapped deserter, wandering
• Behaving irregularly
• Not the regular thing to do wrong with a twitch
• Inconsistent, dodgy criteria I'll have abandoned
• Volatile chap about to desert