From the back of the book:
WHAT LURKS BELOW PHANDALIN?
A beloved town is in unimaginable danger. Whether the heroes are newcomers to Phandalin or are returning after the acclaimed DUNGEONS & DRAGONS adventure Lost Mine of Phandelver, they discover hints of a threat lurking below the town. The heroes soon learn that the cult of a malevolent entity has set its sights on transforming Phandalin into the capital of its evil empire. To save the town from oblivion, the heroes must uncover a nefarious plot and confront the otherworldly cultists.
Phandelver and Below: The Shattered Obelisk is a high-fantasy adventure that begins with the familiar story of Lost of Phandelver and then delves into the perilous Underdark, where dangerous secrets fester and evil is afoot.
A DUNGEONS & DRAGONS adventure that takes characters from 1st to 12th level.