This novel tells the difficult search for an optical phenomenon, the green ray, which can be seen in certain conditions at the moment when the sun disappears on the horizon of the sea.

Sam and Sib Melvill will undertake this adventure to try to marry their niece Elena Campbell with Aristobulus Ursiclos, since the legend says that two people who see it at the same time will automatically fall in love with one another. It is a magical moment when two people discover love at the same time.