His pal Louis wants Merrick to contact his dead vampire daughter Claudia. Like a sulky teenager, Lestat prefers to stay asleep in his room with music playing for most of the novel. And that's the plot. The rest of the book is taken up with flashbacks to David's time with Merrick when he was alive, and Merrick's life generally. The trouble with flashbacks is you know who lived and whether a plan succeeded before you read them.
Flashbacks are action without tension.
At the same time, lots of potential sub-plots and sinister figures are wasted. Even the spectral appearance of Merrick's dead grandmother is a dead end. This wouldn't matter if the characters were interesting and you could get emotionally involved in the story, but they are all phenomenally self-centred and narrow minded. The others all stand around wondering whether it was their fault he did it, and how they would feel without him. Every vampire is the centre of his own little universe.