For former German investigator Henrik Falkner, the picturesque streets of Lisbon's old town have become his new home. He has inherited a quaint antiquarian bookshop from his uncle Martin, along with numerous artifacts that are part of unresolved crimes. One day, he finds a kitschy flag in the shop featuring a rare Japanese fish, a koi. Henrik suspects he is on the trail of a new mystery. A deadly mystery, as the trail leads to ruthless collectors of the valuable fish, who will stop at nothing. Soon, Henrik, along with the beautiful police officer Helena, stands before the first corpse. It won't be the last...