The crew must stop beach frolicking now Toby 'Chefo' Jones plans to propose, for a mayday. It seems a pirate boat, but carries only boat refugees. Alas some splashing water contains microscopic Irukandji jellyfish, whose poisonous bite may be fatal for Chefo and John 'Jack' Jaffah. Chief petty officer Andy 'Charge' Thorpe has something irritating an eye. Petty officer Pete 'Buffer' Tomashevski gets refugee Samira to talk about the scum firing a flair at them and takes their side, unlike Robert 'RO' Dixon, who grumbles he must fill in as cook. Billy 'Spider' Webb is heartbroken when his recruitment 'class clown' Jaffah doesn't make it.

The crew uncovers a people smuggling racket, when they almost collide with a floating shipping container full of North Korean refugees. The Hammersley races to capture the smugglers' ship and save the lives of their human cargo. Kate is wooed by a charming civilian sailor. Meanwhile, Mike is determined to solve the mystery of Ursula's disappearance.