Every third night, Marina Morrison forces herself not to go to bed until after 1am. Otherwise, she risks having to hear her husband, Abel, making love to another woman in the apartment upstairs, in a bedroom directly above her own. "It’s a real struggle for me," 23-year-old Marina freely admits. "But I’m trying to overcome my insecurity and move forward."

While Marina may find the situation challenging, it is also what she has signed up for; she is Abel’s third wife, and shares him with her "sister wives", Suzie, 36, who lives upstairs, and Beth, 37, who has the apartment next door.

The Morrisons – four adults and 12 children – live together at Rockland Ranch, a community of 15 fundamentalist Mormon families, almost half of whom practise polygamy, in a remote corner of Utah. The Rock, as it is known, was founded in the 1970s by Bob Foster, a teacher who had three wives and fathered 38 children.