The Carriage Of A Thousand Ravens

For centuries lonely humans have been going missing. Some return, others don't. Those who do return become a part of a colony of "Wise Ones" who tell the wise truths about who we are individually. No one really knows where these people went, all they know is that they are taken in a carriage pulled by a thousand ravens. But what happens when a man disappears and his younger sister is left alone? What will she witness? Will the carriage take her to her brother? Will she return?