Doctor Who and the Sea-Devils

In 1974, The Sea Devils was released by Target Books under the title Doctor Who and the Sea-Devils.

Cover blurb
Whilst visiting the MASTER, who has been exiled to a luxurious castle prison on a small island, DOCTOR WHO and Jo Grant learn that a number of ships have vanished in the area. Whilst investigating these mysterious disappearances Jo and the Doctor are attacked by a SEA-DEVIL, one of a submarine colony distantly related to the Silurians. Soon they discover that the SEA-DEVILS plan to conquer the earth and enslave humanity, aided and abetted by the MASTER. What can DOCTOR WHO do to stop them?

Cover blurb
Whilst visiting the Master, who has been exiled to a luxurious castle prison on a small island, Doctor Who and Jo Grant learn that a number of ships have vanished in the area. Whilst investigating these mysterious disappearances Jo and the Doctor are attacked by a Sea-Devil, one of a submarine colony distantly related to the Silurians. Soon they discover that the Sea-Devils plan to conquer the earth and enslave humanity, aided and abetted by the Master. What can Doctor Who do to stop them?