Four former Spanish intelligence officers are mysteriously murdered at the same time across the globe. The CNI uncovers that all of them were involved in a clandestine operation known as "Operation Ciénaga," conducted years earlier in Colombia. Zeta, the agency’s top operative, is tasked with tracking down the killer and safeguarding the only remaining survivor of the incident, embarking on what may be his most dangerous international mission to date. To succeed, Zeta teams up with Alfa, a highly skilled Colombian agent who appears to possess deeper knowledge about the secrets of "Ciénaga" than anyone else.