Fierce Kingdom by Gin Phillips

It's near closing time at the zoo and regulars Joan and her four-year-old son, Lincoln, are heading towards the exit when Joan realizes that someone is shooting people. Terrified and desperate to protect her son, Joan heads back into the zoo to find a safe hiding place, but soon, Joan realizes there are at least two people who have no problem killing anything they see. She also wonders how long it will take for the authorities to come and rescue them. Taking place over a few hours, Fierce Kingdom is a page turner that shows the unbreakable bond mothers have towards their children.