Hi Orwellcommie...
Well to present a comprehensive and satisfying account would necessarily mean translating the book!!! However, my knowledge of Spanish is very far from that, as of yet.
A very short version follows here, though not very elaborated since i dont have the time for that: (If anyone read Spanish they should consult this article:
http://www.engels.org/marxismo/marxis2/mar_2_3a.htm).
In the bourgeois History, it is alleged that the conquest of the democratic liberties was the work of Juan Carlos, the King, in collaboration with the left-leaders who were willing to negotiate.
This is a false interpretation. The only reason why parts of the bourgeois establishment conceded in the so-called tyranscision to democracy, was the fact that they were scared of the mighty force that the working class had assumed. In the end of the 1960s the Spanish proletariat had developed a very unique strike-movement that the regime was uncapable of putting down, even through meseaures like executions, torture, arrests, infiltration, etc. The movement was so strong that part of the bourgeoisie now realized that in order to avoid a revolution - that would not just be threatening the dictatorship but the very foundations of capitalism, i.e. the private property - they needed to get control over this movement.
Thats why former supporters of the dictatorship and foreign countrioes who had also supported it now began to talk about a "democratic trancision". Sadly, the leaders of the PCE, the Spanish CP which was by far the strongest organisation in the underground-movement, formed an "association for democracy" which was a popular front with liberals and monarchists, etc. When Franco died in the end of 75 an electryfying wave of strikes and protests broke out affecting allmost every layers of the working class. One of the struggles that culminated was in the Basque Country were an impressing strike-movement took shape linked up by a energetic leadership in which some were from the Marxist tendency, in which´s boards you happen to be in right now :) This movement was, however, faced with massive repression culminating in a massacre on the 3rd of march 1976, where the police brutally attacked an assembly of the strike, with 5 assasinated and more than 80 wounded by gun shuts. Barricades sprung up over the city, etc. In the employers and the authorities were forced to retreat and grant concessions for allmost all the demands. Once again serious reforsm were the by-product of a revolutionary struggle.
The same thing could be set by the trenscuision as a whole. It was a pre-revolutionary situation and had the PCE and the PSOE dared, they could have led the spanish proletariat to power in the years 76-79. But in stead they retreated to compromises and the popularfrontism, that is classcollaboration with the bourgeoisie. The democratic rights were the product of the revolutionary struggles of the working class that forced the bourgeoisie to change the system. They could not rule in the same way that they hasd done for so many yearsm, so they changed the system on the surface. But the same mechanisms, the same organs of the state continued to exists, and none of the torturers, militarists or fascists from the days of Franco were ever persecuted or punished for their crimes. In fact many of the still continue to have posessions in the PP (the big bourgeois party) today.
The Spanish working class that put so much effort in the hope to change societry was ruthlessly betrayed by their own leaders. They could have put an end to capitalism at that time, an event that would have enormous implications and repercussions in Europe and worldwide. They could have changed world history. They did not, and that`s why the task is left to us today!!