Based on a book by T. Llew Jones, this Welsh adventure drama is set in an 18th-Century world of smugglers around Cwmtydu on the Cardiganshire coast. After barrels of cargo are plundered from a shipwreck, the authorities step up their attempts to apprehend Sion Cwilt, the masked leader of a smuggling gang. Meanwhile, Harri Glascoe, who is in love with lower-ranked tavern girl Lucille but is expected to marry a rich landowner's daughter, endeavours to save his father's indebted estate from takeover, and departs on a sailing journey to Europe's capitals to bring back valuable goods. Revelations come to light, as the inhabitants struggle for love and livelihood against corrupt forces.