The Super Spies and the Pied Piper (Super Spies #3) by Lisa Orchard
Book description (from Goodreads) –
Sarah Cole and her sister Lacey are at it once again when they learn their missing parents’ cell phone has been traced to Alden, Michigan. When the FBI declines to continue the investigation, Sarah takes matters into her own hands. She calls upon the Super Spies and they delve into the situation. Suddenly, the teens find themselves immersed in small town intrigue and mystery involving a menacing stranger, who Sarah dubs “The Stalker.”
But when Sarah learns he’s connected to her parents’ disappearance, she’s determined to find out what that connection is. The Super Spies embark on a journey that leads them into a web of corporate corruption at its highest level that leaves innocent victims in its wake. Can they find the proof they need to stop the greedy corporation before it’s too late?
Check out the first two books in the Super Spies series:
Super Spies #1 // Super Spies #2