Rumaan Alam's novel, 'Leave the World Behind,' centers on two families — one Black and one white — who are sharing a vacation home during a mysterious disaster. It explores issues of race and class, fear, and how we respond to crisis. Ken Tucker reviews a new deluxe edition of Prince's masterpiece 'Sign O' The Times.' Craig Foster spent a year diving — without oxygen or a wetsuit — into the frigid sea near Cape Town, South Africa. One octopus began coming out of her den to hunt or explore while Foster watched. He documents their unlikely friendship in 'My Octopus Teacher,' now on Netflix.