Complex sentence: Hannah returns to London after the disastrous trip to Scotland and after telephoning Della she discusses Mitchell, who is described by Della as a "collector", meaning he has various courtesans and prostitutes scattered around the world.
Split into simpler sentences: Hannah returns to London after the disastrous trip to Scotland and telephones Della. They discuss Mitchell, who is described by Della as a "collector", meaning he has various courtesans and prostitutes scattered around the world.