The aliens manage to immobilize Gamera using a special ray weapon, and analyze his mind to determine his weakness. Luckily this is the cue to view Gamera in action against other giant monsters. The first contender is The Quick Freeze Monster, a lizard-like beast who can fire cold. The creature isn't too tricky to defeat but next up is some kind of prototype Rodan. This pterosaur is known as the supersonic monster as it can fire beams of sonic beams, with appropriate 'ziaaaiing' sound effects. This customer proves to be harder work for Gamera and only after he is tossed into a volcano does he realize that he's outclassed.
The aliens note that Gamera saves a fat little boy during the fight and come to the conclusion that Gamera's weakness is his protective nature toward kids. To this end two annoying little pipsqueaks are abducted from the miniature submarine they're larking around in. (I'd explain how they come to be in a miniature submarine but it would require leaps of logic that I won't impose upon you. It makes sense Toho Studios style.)
The aliens manage to land a mind control device on Gamera and force him to obey their orders. Gamera gets stuck into a dam and then turns his attention to Tokyo. At this point the United Nations are faced with a stark choice. Option A: Blow up the space craft, killing both boy scouts but freeing Gamera. Option B: Completely surrender the Earth to alien invaders, in the hope that while billions of men women and children are sold into alien slavery the two boy scouts will be spared.
The United Nations chooses option B, of course. Even the kids realise this makes no sense and beg the military to blow up the spacecraft with them onboard. Luckily one of them is a bit of prankster and knows how to rewire things. After a bit of sabotage the kids escape and Gamera wrecks the spacecraft, which isn't too tricky as it seems to be made of ping pong balls.
The alien leader absorbs the rest of the crew and grows to giant size. He lumbers out to do battle with Gamera while the two kids shout useful tips to their turtle friend like 'Don't let him hit you!' and 'Use your flame!' Gamera makes short work of the would-be conqueror and the world is safe again.
I love giant monster movies but it's a shame that the best bits of this film come from other entries in the Gamera series. All the good battles come from War of the Monsters, Return of the Giant Monsters, and Gamera the Invincible. Some new monster material would have been good but even if you've seen those films, Destroy All Planets is still good fun and as silly as anything you'll ever see in the genre. Obviously if you have no love of giant monsters then there's absolutely nothing here that will change your mind. The plot is daft to the point that you'll laugh out loud at the actual logic (or lack of). But it was obviously a film made for children and should be regarded in that light. If you're like me and find yourself chuckling whenever the likes of Gamera makes an appearance, then this film is full of enjoyable moments and at least has some good fight scenes to enjoy, including of course the final battle with Viras the starfish/squid alien leader.