23

In this moment, you want nothing more than to hug Brett and tell her that her safety is far and away the most important thing to you.

"Hey, look at this." Brett's gone to the front of the Land Rover and is staring at something. You circle around to join her, only to be brought up short.

Before the right front tire, blocking the passenger door, lies a second prehistoric flier. It has the same sword-like beak as the first one, though it's considerably smaller and lacks a head crest. Dark blood from one of its crumpled wings has gushed onto the bumper, and spatters glisten across one mustard-yellow fender.

You gape at its closed eyes and inert form as silence descends, wishing you could redo your arrival. If only it were possible.

The laws of temporal physics dictate that you can never revisit any time and place you've ever been before, including anywhere you've ever lived. You get just one shot at existing in any given set of space-time coordinates. No paradoxes allowed. No coming back here five minutes before today's arrival. Or five days or five years, for that matter, with the intent to stay here until today. Setting the time machine to do so will produce a slew of blinking red lights and error codes. Here's the great irony of actual time travel: it permits no do-overs, no Groundhog Day.