Book review This Motherless Land By Nikki May Mariner Books: 352 pages, $30 If you buy books linked on our site, The Times may earn a commission from Bookshop.org, whose fees support independent bookstores. Loosely based on Jane Austen’s most explicitly political and critically controversial novel, “Mansfield Park,” Nikki May’s “This Motherless Land” explores clashes of custom and class in …