Book 4 Synopsis Focused on BellatrixUnfortunately, Bellatrix only briefly appears on two occasions within this book. The first occasion occurs whilst Harry is viewing some of Dumbledore's memories within his pensieve. During this viewing, he comes across Bellatrix's Wizengamot trial before she gets placed in Azkaban. On trial for torturing the Longbottom's using the Cruciatus Curse, she is escorted into the trial by Dementors along with Rodolphus, Barty Crouch and Rodolphus's brother. Bellatrix remains silent for most of the trial (Barty Crouch is the most vocal - pleading to his father) however as the trial ends, she proclaims her loyalty to Voldemort. She is also mentioned within book 4 by Sirius when he is listing Severus Snape's friends from his time at Hogwarts. The list includes the "Lestranges".
Book 5 Synopsis Focused on BellatrixHer first mention in book five occurs whilst Harry is staying in 12 Grimmauld Place, his godfather's family home. Kreacher, the old house elf that used to serve the Black family before Mrs. Black died, was found to have a picture of Bellatrix hidden in the room where he salvaged any of the old Black family heirlooms that he could find. From the way the picture was placed, it was clear that Kreacher was quite fond of Bellatrix. Bella is next mentioned in book 5 within a Daily Prophet article that reported that several Death Eaters had escaped from Azkaban. Bellatrix's picture is described by Harry in the following way. She glared up at him through heavily lidded eyes, an arrogant, disdainful smile playing around her thin mouth. Like Sirius, she retained vestiges of great good looks, but something - perhaps Azkaban - had taken most of her beauty. It is at this point within the book that we realise that Voldemort is as powerful as he ever was, now that his strongest supporters - Bellatrix included - were now outside the walls of Azkaban. The third and final time we come across Bellatrix in book 5 is her largest part as yet. Bellatrix is one of the Death Eaters present in a trap set out by Voldemort to lure Harry into the Department of Mysteries so as to retrieve the Prophecy. During the inital confrontation, Bellatrix and several other Death Eaters first try to play mind games with Harry in order to get the Prophecy from him in a non-violent manner. When these attempts fail, however, and Harry trys to escape with his friends, the confrontation turns into a battle. During the battle, Bellatrix managed to capture Neville Longbottom and in order to try and convince Harry to give her the Prophecy, she begins to torture Neville using the Cruatius curse (the very curse she was put into Azkaban for using on Neville's parents). This didn't last long, however, as members of the Order of the Phoenix soon turned up and began to fight the Death Eaters instead. Within this second battle, Bellatrix shows her true ability with a wand as she manages to badly maim Nymphadora Tonks and Kingsley Shacklebolt, as well as infamously killing Sirius Black (her cousin). Once Sirius was killed, she escaped the Department of Mysteries, along with Dumbledore. However, following her was Harry who was outraged at the killing of his godfather. After several other confrontations, including one in which Harry attempted to use the Cruatius curse on Bellatrix, Harry finally confessed that he had dropped the Prophecy during the battle in the Department of Mysteries. Once this was known, Voldemort then appeared, determined to kill Harry once and for all. Dumbledore, however, quickly came to Harry's rescue and the two powers battled until Voldemort finally retreated, taking Bellatrix with him.