Lo spirito del fiume

On the Blue Queen, a boat that travels the river, disturbing apparitions occur: is it perhaps haunted by ghosts? This is what Zagor, Bat and Bing Batterton must discover, as they investigate the nature of the mysterious presences. But there are also much more real dangers on that ship.
A gang of smugglers operates on the Blue Queen, and one of them is the singer Lorna, to whom Zagor seems attracted. When Lorna is kidnapped by Urmak's Indian raiders, our hero frees her. But he still has to find out who the mysterious ghost is... It is a professional gambler whose father had been killed a few years earlier by the captain of the boat.
The captain will be punished by his own remorse, which takes the form of a spectral figure that torments him in his sleep and causes him to have a cardiac arrest...