U1-2-3: Saltmarsh Trilogy

The Saltmarsh Trilogy comprises U1: The Sinister Secret of Saltmarsh, U2: Danger at Dunwater, and U3: The Terrible Title aka Final Enemy. These were released annually 1981-3. "U" stands for "United Kingdom". All three are credited to "Dave Browne with Don Turnbull" - why the preposition, maybe some Limey thing.

Anyway the series was all deemed good at the time. 2e interpolated an adventure between U2 and U3; then 3e added sequels. These all got translated to 5e and fleshed out, and competently. So competently, we're not going to spoil it all here for a change. Refer to Ghosts of Saltmarsh.