After learning about the Substance known as R at the PCL in Chapter 3, Tim and Pikachu will look to Find the accidental creator of the chemical, the man that goes by John Waals. In order to do this, they will first need to speak with Mr. Baker and Mr. Holiday at the Baker Detective Agency to begin Chapter 4. By doing this, they will learn that John Waals is living on Cappucci Island. From here, Mr. Baker will offer Amanda to take you there on her boat.
Once reaching Cappucci Island, you will need to investigate to learn of John Waals' whereabouts. By talking with Louise, one of the resort directors back in Ryme City that is visiting the island, she will tell you that John Waals lives in one of the houses in the village. However, along the way, you will come across an injured Ducklett. As you do, an aspiring Pokemon Ranger called Milo will come and help the Pokemon. From there, Milo will personally escort you to John Waal's house, as he is actually the protege of the man himself.