in the dark (?.)

• at night
• behind the curtain
• behind the scenes
• behind the veil
• benighted
• by night
• covertly
• dark
• darkling
• in a corner
• in a whisper
• in darkness
• in hidlings
• in secret
• in the background
• in the night
• nobody the wiser
• secretly
• sotto voce
• sub rosa
• under the breath
• under the rose
• undercover
• underground
• with bated breath