This was always going to be a bit of a comedown after those first two dazzlers. Still, Doctor Who has always been a sci-fi pick 'n' mix. Let's judge this episode on its own merits - and there are several bobbing among the ankle-deep bilge.
Just think of the cast and crew labouring gamely over several chilly nights back in February in Charlestown. On screen you really do believe that this brigantine, the Phoenix of Dell Quay, is way out on the ocean, not safely moored in a Cornish harbour, overlooked by paparazzi and spoiler-fixated fans. The moonlight and mist - whether faked or real - make for superbly atmospheric cinematography.
Playing the alien siren, model-turned-actress Lily Cole may look more stoat than fish, but is magnificent bathed in an ethereal, turquoise shimmer, zooming out of the water and any other available reflective surface. However, like the mermaids of maritime mythology, she makes fools of men - demanding more ardour than these actors can convincingly muster on a shrivellingly cold night shoot.
I can watch Hugh Bonneville in anything. Splendid in Iris and Downton Abbey, he was the best thing about the limping Twenty Twelve and even funnier in woebegone Bonekickers. It's plain he's relishing the role of Captain Henry Avery. He's gone to the effort of growing a beard; alas, his character needed time to grow, too.
Reasons for Avery "turning pirate" are left hanging in the night air. He's an ex-naval officer, so Bonneville remains plummy and far from your typical ooh-aar cap'n. Indeed, Avery steadfastly avoids most of the cod piratical tics, although the narrative ticks off some Treasure Island essentials: scurvy knaves, cabin boy, the black spot…
It's not made abundantly clear in the dialogue, but Avery was a real-life buccaneer, notorious in the 1690s, who was never captured. It was thought he'd retired with his booty, but now we know "the treasure of the Moghul of India" was dumped overboard before Avery sailed off into space with his band of rogues! In a minor way, this story acts as a prequel to a long-ago-wiped 1960s adventure, (The Smugglers). A 17th-century romp with William Hartnell's Doctor, also filmed in Cornwall, it saw Avery's former shipmates hunting down his hidden stash of gold. I think I know which drama I'd rather have been watching tonight.
At times Steve Thompson's episode hobbles along like Blind Pew, bunging in the underfed subplot of Avery and his son, showing the Doctor implausibly abandon the Tardis… Perhaps what irks most is the mystery of the vanishing crew. Fine, the BBC budget can only press-gang six or so sea dogs into service, and a line establishes that the rest have been picked off by the siren. But not all of the men that we do see are properly dispatched.
Crucially, what happens to the boatswain (ex-EastEnder Lee Ross), the most vocal and unpleasant of Avery's sidekicks? One minute he's holed up with Amy and Rory in the armoury, then he disappears from the narrative entirely until the final reunion. How did he get aboard the siren's "sickbay"?
If you're looking for a watertight plot, that ship has sailed. But belay any doubts, me hearties! Next week's instalment, tantalisingly entitled The Doctor's Wife, will catch the wind.