Solve the Riddle

Harry's in the past. There is no 'Lord' Voldemort. However, if he expects things to be easier just because he's older and Riddle's younger, he's going to be sorely disappointed. Harry's never been one for giving up, but neither has Riddle, and as they both are forced to work together- in more ways than one- the stakes slowly change. [Time travel, Dimensional travel, fem!Riddle]