The story has a Christmas setting and features Zantafio and Seccotine. Stripspeciaalzaak also provides a blurb:
Fantasio’s cousin, the sneaky Zantafio, accidentally comes into possession of a large batch of diamonds. The police is looking for the precious stones, and some way to smuggle them across the border is needed. Meanwhile, the Count of Champignac has built a device to solve the overfishing of the seas. Seccotine comes along to write an article about the test run. And Spirou and Fantasio? They have rented a vacation cottage by the sea to celebrate Christmas and to work on an end-of-year summary for the magazine. But of course things don’t work out that way.
Like the first album in the series, Happy Family, this one will also be published in a deluxe hardcover edition as well as the regular softcover version.
Update: Dupuis are in the process of updating their website design, and the Dutch version is currently a bit broken, but here is the official page for the album, with slightly more detail in the blurb. (The diamonds are Jewish; Spirou & Fantasio witness the theft but can’t arrest the suspect because there’s no proof, with the jewels have vanished; the Count’s invention is made for a mysterious Mr. Wobbel; and the test is being led by a Captain Buiswater van de Kibbeling.)