We start off in 1776 on Captain Clegg's ship, where his bosun is reading off the punishment of a crewmember (Milton Reid) who apparently raped Captain Clegg's wife, for which crime the man will have his ears sliced off, his tongue cut out and marooned with no food or water on a deserted island. Did I mention we only saw the Captain from behind and in shadow?
Almost immediately we jump to 1792, to the Romney Marshes, where an old geezer (Sydney Bromley) has made the mistake of taking a late night walk. Unfortunately, a bunch of ghostly, skeletal horseman (watched over by a scarecrow with human eyes!) have also decided to go out tonight and frighten the man to death.
The next day, Captain Collier (Patrick Allen) and about a dozen British sailors show up in Romney Marshes to investigate a smuggling ring. They've timed their visit so that the villagers are in church and won't have time to hide their smuggled French alcohol. However, the normally verbose Reverend Dr. Blyss (Peter Cushing) decides to cut his sermon short and gives a signal to certain churchgoers to leave early. It looks like Captain Collier might be up against more than the normal crude smuggling operation. On the other hand, Captain Collier brought along a certain tongueless, ear-less gent with a good memory of old comrade.
As you can imagine from that description above, Captain Clegg is more of a crime thriller with horror touches. If I had to be that annoying high concept movie pitch guy, I'd suggest The Untouchables meets Tombs of the Blind Dead. The story is very loosely based on Dr. Syn by Russell Thorndike, which was also the basis for the 1937 film Dr. Syn and the 1962 Disney tv special (!) The Scarecrow of Romney Marsh. The character is also referenced in the League of Extraordinary Gentlemen graphic novels.
I can easily see why Hammer would make this film. It looks like horror, but allows them to move into less heavily exploited territory and explore beyond the normal horror pantheon.
And the movie is quite fun. Cushing does a good job of jumping between the poses of the goodhearted Reverend Blyss and the colder, more pragmatic Captain Clegg, without making it easy for the viewer to decide which one is the "true" man. Allen is also fascinating as an iron-willed naval officer who can be as vicious, if not more so, than his quarry. Oliver Reed shows up as the male ingenue and manages to find a little depth to an under-written character. The "marsh ghost" costumes are creepy and effective while remaining credible as homemade outfits.
On the other hand, Clegg doesn't really come together. The cat-and-mouse game between Allen and Cushing is well done, but too much of the movie is about the sailors and smugglers sneaking around rural England. It's pretty easy to guess at Cushing's former identity early on, so there is no mystery. And while Oliver Reed does a good job with what he has, he barely registers as a character for the first half of the film and he doesn't get to do that much afterwards. And the "ghosts" only show up twice for a few minutes each time.
I wouldn't be surprised if horror fans left disappointed and no one else showed up. When Hammer films are discussed in books or websites, Clegg gets left out (even when someone will go so far as to cover Dracula AD 1972!). If anything, it seems like the story would do better now that Pirates of the Carribean has opened the door for pirate/thriller hybrids, although the supernatural elements would need to be seriously ramped up.
Thematically, the movie keeps raising ideas like the way the government regulation is more likely to hurt common people than help or the games people play with identity or the secrets hidden beneath the surface of idyllic rural life and then casting them away to focus on an uninteresting mystery. I certainly didn't expect a fifteen minute speech on Milton Friedman or John Keegan, but there were certainly relationships and plot points which would have delved deeper and that got rushed through or ignored.