Catherine Gremory can be found in the North-East area of Sentinel Island, inside the skeleton of a huge long-dead whale. She explains that she is studying the ancient whales.

If you have already met Jonah and accepted his quest The Old Ghost and the Sea, Catherine will give you an amulet which once belonged to Jonah and is required to complete that quest.

She will also give the side-quest, The Writing on the Whale.

Reading her mind will reveal the password to the Gremory family jewels, whose location is obtained from mind-reading her brother, George Gremory.