La Club de la Marcia en la Lago Negra

La Club de la Marcia en la Lago Negra is the fourth book in the La marcia nonconoseda series, written in Lingua Franca Nova. Worried after their friends' previous summers repeatedly made the news, Joan's parents send the whole group — Elisenda, Luca, Eneko, and twins Irati and Itxaso — to a supervised youth camp by the Lago Negra instead of back to the Vileta de la Marci. Undeterred, the friends slip away to explore a ruined medieval castle on an island at the centre of the lake, where they stumble upon a mysterious nighttime delivery hidden in the castle's old prison. As they investigate further, the group is drawn into a conspiracy involving people closer to the camp than they expected, forcing them to rely on their wits and each other to get out safely. The story was inspired by the real Laguna Negra in Soria, Spain, and by its legends, including the one told in Antonio Machado's 1912 poem "La tierra de Alvargonzález."