Don’t know how characters got to this point. As a writer of flash fiction, there’s not enough room in your story to have a back story. Last night, I was watching the new series from the producers of the The Walking Dead television series. The new is called, Fear the Walking Dead. The majority of the episode was backstory, and there were only three zombies for the hour and half the show aired. We learned about everyone one of the main characters, but the zombies for the first episode were in the background. Our protagonists only fought one zombie. Why? Because the writers and producers of the show knew they had time for the zombies and to introduce the monsters gradually. In the original TV show, The Walking Dead, the main character, Rick woke up in the hospital and basically had to fight the zombies from the first few minutes of the episode’s beginning. He throw into the action. I think the second approach is better here, and Walking Dead is better than Fear the Walking Dead.
Which method is better, backstory or no backstory? In a novel, there’s plenty of time for backstory. As a writer, it’s up to you to make it work. In flash fiction, there’s no time. Have the plane crash, the spouse leaving, being fired from the job, or the barbarians storming the city’s gate at the front end of the story. Or someone just left the front door open… It will set the urgency for the story and draw the reader in right away.