A Sound of Thunder

Set in 2055, humans have mastered the art of time travel. The baddie appropriates the technology to send groups of hunters back 65 million years to shoot a dinosaur. After one problematic hunt, things start changing in the present, and they realise that they disturbed the timeline, and now nature is following an alternative evolutionary path, spelling disaster for humans. So the hero and heroine go back to the past again to try and fix the mistake... which has other repercussions. And trying to fix it again also doesn't work...