It’s 1865. In the closing days of the American Civil War, a Confederate Ironclad gunboat — a sort of squat, floating tank with faceted, armoured contours suggestive of a modern Stealth fighter aircraft — steams out of the heavily besieged Southern port of Richmond with a secret cargo and heads off into the dark to points unknown.

Cut to the present. The mysterious vessel has become the stuff of legend, having not been seen again since the night it left harbour, 140 years ago. However, Nigeria-based marine salvage expert Dirk Pitt (Matthew McConaughey) is obsessed with tracking down the Ironclad’s wreck.

All his dives off the American coast have drawn a blank, but when a Nigerian dealer in ancient contraband sells Dirk an incredibly rare coin — a Confederate gold dollar – the adventurer smells paydirt. The Ironclad's captain was known to have such a coin — one of only five — in his possession.

Dirk still can’t get his head round how a boat built for nothing more fierce than US coastal waters could have crossed the Atlantic a century-and-a-half ago, but he suspends his disbelief and heads off on the coin’s trail, up-river into the north-west African interior.

For company he has good buddy and fellow salvager Al Giordino (Steve Zahn). Incidentally, the pals are former special-forces cronies, which bodes well for them in fisticuffs to come.

Hitching a boat ride with them is World Health Organisation medic Eva Rojas (Penelope Cruz) who is on a quest of her own — she’s trying to track down the source of a baffling disease devastating the local population.

And is there more to this old-tub, new-bug mix? Stir in a gun-crazy dictator and his faceless hordes, a shady technocrat and his faceless hordes, lots of unpredictable Tuareg tribesmen, lots of unpredictable Tuareg camels, and a vast, secret industrial installation deep in the desert and you’ve got the sort of components that keep the plot on a constant simmer, if only occasionally on the boil.

The problem facing rip-roaring adventure yarns like Sahara is that they rely on a constant procession of set-piece, action sequences if they are to to deliver the goods, and these have to be grand-scale or pretty inventive to excite the jaded palate of current cinema audiences.

We’ve all grown up on a diet of Indy and Bond movies, and we expect plenty of colossal, intricate bangs for our bucks. Sahara doesn’t have these, with the action fairly underwhelming at every turn.

The intriguing storyline also suffers from having more loose ends than a thousand Bedouin tents have guy ropes. Based on a Clive Cussler novel, one can’t help but feel a lot of his pages have ended up on the cutting-room floor.

Sahara’s saving grace is the cast. The chemistry is there between McConaughey and Zahn, and their double-turn as wisecracking, jawcracking brothers-in-arms-and-artefacts steals the show. Cruz is also a mighty presence, if for nothing more than her beautiful face. I’d cross a desert to gaze upon it, even aboard an unpredictable Tuareg camel.

However, one actor choice did have me choking just a little on my choc ice — Coen brothers regular William C. Macy plays retired admiral James Sandecker, Dirk and Al's cigar-chewing boss aboard the salvage team's mother ship anchored off the Nigerian coast. He's a sort of straight-man foil to his devil-may-care lieutenants on shore, with the camera frequently switching back to him on the bridge of his ship, gnawing anxiously on ever-larger portions of bulkhead with every new report of escalating grief from the interior.

This is an imaginative piece of casting, considering that Macy normally plays hangdog, underdog runts. If he'd popped up here as James Sandecker, Deck Scrubber Third Class, Retired, I wouldn't have batted an eyelid. But an ex-admiral? Blistering barnacles!

VERDICT: The unravelling of a great riddle? The untwining of a great lot of twaddle, but mildly enjoyable all the same.

Three stars

IT’S surprising that The Merchant of Venice, being one of Shakespeare’s most recognisable plays, has not been filmed since the days of silent cinema.

The reason why filmmakers have shunned the work for the best part of a century is clear. The character of Shylock, an anti-Semitic caricature who demands his pound of flesh, is an ugly and difficult person to have as a film’s centre.

Yet thanks to a captivating performance by Al Pacino, a well known Shakespeare enthusiast who seems to cherish playing the role, the character seems less of a stereotype and frighteningly real.

Unlike many Shakespeare adaptations these days, the film keeps to the play’s original context, 16th century Venice, and looks great, with director Michael Radford having paid painstaking attention to detail. Ultimately though, the film, at 2 hours 20 minutes, is way too long and the ending is far-fetched, to say the least.

VERDICT: Well done, but for Shakespeare enthusiasts only.

Three stars

(15, Paramount)

TO remake a classic film, and in particular one which is still so fresh and disturbing today, is never a good idea.

And giving it to director Jonathan Demme who failed quite spectacularly with his last film, a remake of Charade, would seem like an act of folly.

But Silence of the Lambs director Demme is perfectly suited to this material, which is one part detective story, one part horror.

Denzel Washington is in the Frank Sinatra role of a former soldier who served with a presidential candidate. Since the last war he has been troubled by dreams of scientists experimenting on him.

It’s another interesting choice of role by Washington, who acts like a crackpot for much of the film.

Since his Oscar win for Training Day, Washington seems driven to more edgy parts, not least as an assassin in Man on Fire, which has also recently come out on DVD.

Meryl Streep is suitably crazed as the mother of the presidential candidate (Liev Schreiber) and Demme's bag of directorial tricks, gives the film urgency and danger.

This is a fine remake indeed, with added potency as a result of the recent Gulf War, and its theme of corporate power over elections seem more relevant today than ever.

EXTRAS: Commentary, deleted scenes and two making-of featurettes.

VERDICT: A remake which almost matches the original.

Four stars

The boxset will include a new two-disc special edition of Bullitt, along with The Getaway, Never So Few, Tom Horn and The Cincinnati Kid, one of McQueen’s most underrated films, making its DVD debut.

The improved edition of Bullitt, which will also be available separately, includes a director’s commentary and three documentaries, including the DVD debut of The Cutting Edge: The Magic of Movie Editing, which includes contributions from Spielberg, Lucas, Scorsese and Tarantino.

The Getaway and The Cincinnati Kid will also feature director’s commentaries as well as other special features.

The boxset is priced £49.99, with Bullitt and The Getaway available separately, priced £19.99 and £15.99 respectively.

NOT getting as good DVD treatment is Mike Leigh’s Vera Drake, which comes out at the end of this month.

The Oscar- nominated drama about a kind- hearted woman carrying out illegal abortions in the 1950s will be released with no director’s commentary and just a scant cash and crew documentary in its extra section.

A worthy film undoubtedly, but a bleak one which I won’t be in a rush to sit through again.

For those of you with more patience than me, Vera Drake will be available from Momentum Pictures, priced £19.99 on April 25.