Adventures in the Sea of Silence, North-Eastern Islands

Philip, Jack, Dinah, and Lucy-Ann are very happy to get the opportunity on holiday on the northern British coastal islands. Moreover, they are also accompanied by Kiki, the cerewet and Bill, while having to "disappear" from their enemies. But the holiday turns tense. A mysterious airplane roam around the island and drop something into the sea. Then there are people who come to Muffin Island and kidnapped Bill. What mystery is going there?
How can they pass themselves from that island and save Bill from their kidnapping grip?
Item price includes shipping fee that should be borne by the buyer.