It's time to say goodbye.

The third chapter of the blockbusting Night At The Museum franchise has lost two of its greatest special effects - Mickey Rooney and Robin Williams - in the past 12 months. So it's fitting that Secret Of The Tomb should be an action-packed adventure punctuated with dewy-eyed farewells and warm-hearted reminiscence.

Shawn Levy's picture is a fitting swansong, reuniting most of the protagonists from the original for a final transatlantic hurrah.

The script adds father-son bonding to the mix and a new Neanderthal called Laa (Ben Stiller), who is partial to munching on polystyrene foam.

For the most part though, familiarity with the series' larger-than-life characters breeds contentment.

The third chapter opens in 1938 Egypt, where adventurer Robert Fredericks (Brennan Elliott) and his 12-year-old son CJ (Percy Hynes-White) stumble upon a burial chamber.

"If anyone disturbs this tomb, the end will come!" proclaims one superstitious local.

Undaunted, Fredericks empties the site of its priceless artefacts, dividing the treasures between New York and London.

Fast-forwarding to the present day, the magical Tablet Of Ahkmenrah, which brings to life the exhibits of the American Museum Of Natural History, is losing its power.

Security guard Larry Daley (Stiller) recognises the repercussions for his display case chums and enlists the help of museum director Dr McPhee (Ricky Gervais) to ship the tablet to the British Museum in London, home of pharaoh Merenkahre (Sir Ben Kingsley), who fashioned the tablet in honour of his son Ahkmenrah (Rami Malek).

Larry heads for the British capital with his son Nick (Skyler Gisondo) and several stowaways: Theodore Roosevelt (Robin Williams), cowboy Jedediah (Owen Wilson), Roman general Octavius (Steve Coogan), Attila the Hun (Patrick Gallagher), interpreter Sacagawea (Mizuo Peck), Laa and Dexter the capuchin monkey.

Aided by dashing Sir Lancelot (Dan Stevens) and hindered by local security guard Mindy (Rebel Wilson), Larry races against time to restore the tablet's lustre before the magic dissipates forever.

Night At The Museum: Secret Of The Tomb milks our affection for the characters without exhausting our good will.

There's nothing innovative in the third film but good humour and sweetness prevail, and the script continues to have fun juxtaposing the modern and ancient worlds like when Sir Lancelot asks Nick, "Have you ever held a blade?" and the teenage responds, "Only in World Of Warcraft."

London looks splendid through Levy's lens, accompanied by a predictable yet rousing chorus of The Clash, and an extended cameo by a Hollywood superstar during the frenetic denouement is a treat.

Stiller seems to have tears in his eyes for most of the second half, relying predominantly on co-stars to lasso the laughs.

When Williams' waxwork President acknowledges the end is nigh and softly remarks, "You have to let us go," it's hard not to get a little lump in your throat.