We meet him as he receives news of the sudden death of the previous Pope. The early chapters introduce other characters and this part is, perhaps inevitably, a little slow. The real drama only begins once the election itself is under way.
Initially there are four men who have a realistic prospect of election. One of these is favoured by Lomeli, but as the balloting continues it becomes increasingly clear that the choice will fall on one of the others. But all three have flaws, some of which are obvious to Lomeli initially while others emerge later. Lomeli himself is widely respected but he is painfully aware of his own spiritual conflicts, which increasingly come to the surface as the Conclave proceeds.
Tension builds nicely as voting continues. The final result doesn't come as a total surprise—it's fairly well signalled—but there is a twist in the last chapter that strains credulity almost to breaking point, although I suppose it is just about conceivable.
Apart from the thriller element the book is worth reading for anyone who is curious about how a papal election works. I assume the details are reasonably authentic. In his acknowledgements Harris says that he was allowed to visit the locations used in Conclaves that are normally closed to the public, and he had advice from two named Vatican officials. He consulted other prominent. Catholics, including a cardinal who had actually participated in a Conclave, although these conversations were off the record. Harris hopes that those concerned were not too appalled by the result.