When is a musical not a musical? When it’s The Mistress Cycle, a new work described as a ‘song cycle’ illuminating stories of passion, sacrifice and spirit in the lives and loves of five notorious mistresses. The historic females, who rose to positions of power and influence through their liaisons, range from 20th-century sexual adventurer Anais Nin to 16th-century Diane De Poitiers (mistress of King Henri II) to Ching, a teenage concubine in 12th-century China. With music by Jenny Giering and lyrics by Beth Blatt, The Mistress Cycle has won a slew of honors in theater development circles. This regional premiere runs through Jan. 5 at Apple Tree Theatre, 1850 Green Bay Road, Highland Park; 847-432-4335; $38-$48. Photo by Michael Brosilow