A Slip In Time

Harry Potter had been too weak, he put up one hell of a fight but it wasn't good enough.
With one singular flick of a wand and two words mumbled, his body crumpled to the floor: Lifeless and limp as his eyes stared without seeing.
Screams of terror and sorrow sounded throughout the courtyard.
None of them strong enough to bring back their saviour.

What happens when four unlikely individuals find the rare occurrence of a time turner and go back in time with a mission, a mission to save the world and the many who died at Voldemort's grasp.