Head north, chasing after Tobli until you reach the South Wharf.
Go back the way you came until you spot Tobli again.
When he zooms past on a scooter, go back north again to South Wharf.
Cross the moonflow on the shoopuf and head towards Guadosalam.
Just before reaching Guadosalam, you'll catch up with Tobli.
Your reward is the Black Tabbard grid.
Mission Complete!