Submerged (Submerged #1)

On the night of the biggest storm in New York City history, Elysia Puente gets a call from her estranged little brother Angel, terrified, begging for help. When the call cuts out suddenly, despite the bad feelings between them, Ellie rushes into the night. Finding his broken phone in front of a barricaded subway station, Ellie follows echoes of her brother into the sinister darkness of the underground, desperate to find him before it's too late.