Hot on the heels of last week's first contact with hostile underwater humanoids comes a series of missile attacks on the WASP's Marineville base. So far the attacks have all been intercepted by WASP missiles (lovely red and yellow things crying out to be made into ice lollies - the colour scheme wasted on British viewers, of course), but the crew of Stingray (now augmented by the enigmatic Marina, though what purpose she's meant to serve other than decoration isn't quite clear) are sent to find out where the incoming missiles are being launched from.
In the rough area of the missiles' origin, they find an abandoned island, but it all looks pretty harmless ("How about you, Marina? Do you see anything" asks Troy. If she does it's unclear how she's supposed to tell him what it is) - until they start to head off elsewhere, when a dirty great missile emerges from the island's summit.
Finding their way into a grotto beneath the island, Phones and Troy go to investigate on flying chair things similar to the ones in Fireball XL5 (and Space Patrol, for that matter), encountering a strange purple light which turns out to be a paralysing ray - and, also, apparently, a perspirising ray (how I've missed the sight of sweaty puppets!).
The ray sends the pair into a slumber from which they awake to find themselves prisoners of a strangely Grecian-looking pair of beings who delight in the names of Nucella and Chidora (it's not stated that they've any connection with Titan, so it could just be that all the undersea peoples have turned hostile toward the land-dwellers at once - although they seem to know Troy's name, so perhaps Titan's told them all about him). Despite their fancy appearance they're refreshingly blunt: "Shut up and listen, Tempest!"
Nucella, the leader (he's got a beard) announces that Troy will help him to destroy Marineville - he's holding Marina captive (she doesn't look especially distressed - as usual she just looks very bored) and will electrocute her if Troy doesn't reveal the frequencies that will allow his missiles to avoid the interceptors (why would he assume Troy would know this? It seems pretty specialised). As Phones points out, it seems pretty obvious that the lives of thousands of people are worth more than just the three of theirs, but nonetheless Troy gives in and reveals the required information.
The Stingray team are locked up while the baddies set to work, but Troy swiftly comes up with an escape plan. Demanding a button from Phones' uniform (how can you trust someone who won't even sacrifice his own buttons?), and instructing Marina to rip up a cushion cover.
With these uninspiring components, Troy knocks up a contraption to grab the key which the idiotic Chidora left on a nearby table (these baddies may be pretty dim but I like their taste in decor). After a few attempts he finally gets it.
Then he and Phones are off to prevent the missile from destroying Marineville - "One false move and we'll all be blown to paradise!" - and then back to the cell before the villains know they've been gone.
At dawn the next day, the missile is launched. Nucella and Chidora watch in eager anticipation on their fancy screen as it gets ever closer to its target.
The interceptors fail to stop the missile? Could this be the end for Marineville? Well, no, as it happens. The missile hits the ground without exploding and Commander Shore sends a dinky little bomb disposal van out to deal with it.
The Commander's astounded when he's told that the warhead of the rocket was disarmed - and Troy left a little note in there telling him where he's being held.
WASP planes launch an attack on the villain's base, and as their pretty devices start to go up in smoke they're forced to surrender. They're hauled aboard Stingray as captives and their base is comprehensively destroyed.
The episode ends with a customary naff comedy bit as the luckless Phones is told off for having a button missing from his tunic. I bet that Troy Tempest set him up deliberately, the bastard.