Although this whole British series is very good, there are a few that are outstanding in plot, drama, and pure genius. This is one of them.
Holly Adam's dad receives the use of a canal boat for free, for a week, from a grateful client who loves the furniture made by Mr. Adams for him. So of course he takes the three excited Mystery Club girls- Holly and her friends Tracy and Belinda- plus her London friends Miranda and Peter. It's going to be a nice quiet loop on the canals for a week. Right? Wrong! The trouble starts when they stop to help an injured girl along the canal and agree to take her on to her home town. She knows a shortcut, so they follow her directions onto a deserted rarely used narrow canal with a tunnel where they- yep, get stuck. The motor cuts out and then the girl, "Jane Smith", runs off. As they follow her to a guarded compound, they realize that something is very wrong. Before they know it all 5 teens plus Mr. Adams are prisoners. Luckily these kids are plucky with a lot of tricks up their sleeves.