Lovers of investment intrigue, Grinnell College, Younkers and Des Moines development should be interested in “Mentor: Life and Legacy of Joe Rosenfield,” a new book about Younkers chief, Grinnell alum and trustee, businessman, lawyer, and philanthropist Joe Rosenfield. Former Grinnell President George Drake, himself a Grinnell legend, spends more than 300 pages laying out Rosenfield’s high-profile career, including gutsy investment antics with his friend, billionaire Warren Buffett. Both served as Grinnell trustees, with Rosenfield working on the board from 1941 until he died in 2000. In that time, the Grinnell endowment grew from $78,000 to more than $1 billion. Rosenfield also amassed a 5% share of his beloved Chicago Cubs, bankrolled Jim Cownie’s Heritage Cablevision and changed Iowa in ways many may not know. Cownie backed this book, published this month by WriteBrain, part of Business Publications Corp., parent of the Business Record. Buffett wrote the foreword. The book includes references to BPC Chairman Connie Wimer, who is a Grinnell trustee.