Nothing beats a vacation with your best friend - that's what Holger and Pebble are thinking. How nice that Pebble's sister lives by a lake in the mountains, just a train ride away. There is so much to do and explore. But Holger starts missing home and doesn't really want to do "pebble stuff" such as bathing in the ice cold lake or rolling down a mountain ... Three is a party! Not only because the readers meet a new friend in this book, but also because this is the third adventure of Holger and Pebble.