Return to the ship. When the professor says that you will run out of oxygen use the vitriol on the moon rock. You now return from the moon. Return to Piers House. Piers House Give the catnip to 73.
Piers catches the mouse.
Go to Mirabella's. Mirabella's House Give the mouse to Mirabella. The ring falls on to the grass to the right of Mirabella. Pick up the ring. Take the cab to Whitechapel.