"Buffy the Vampire Slayer"'s loss was...someone's gain. When David Boreanaz left the cult series following Season Three, and his character acquired his own spin off, BtVS suffered a loss from which it would never fully recover. Cordelia (Charisma Carpenter), who went with Angel, could be replaced, but Angel himself left a void that was never filled, despite the best efforts of Mark Blucas (Riley) and James Marsters (Spike). Luckily, the spin off that drew Boreanaz away from "Buffy" would become as good, if not better, than BtVS in it's prime.
Season One of "Angel" begins with Angel moving to Los Angeles, and quickly picking up two helpers in the fight against evil; fellow former resident of Sunnydale Cordelia Chase, and emissary of the mysterious Powers That Be Allen Francis Doyle (Glenn Quinn). Doyle receives visions from the Powers, directing the team at Angel Investigations (Angel's detective agency) to help. Doyle bit the bullet nine episodes in (Quinn left the series for reasons that have always been vague), and his replacement was a third former "Buffy" castmember, Watcher turned rogue demon hunter Wesley Wyndham-Price (Alexis Denisof. Of all the characters to join the cast over the years, none were more significant than Denisof. The last three episodes also featured J. August Richards as Charles Gunn, who would join the cast in Season Two. Recurring characters included; Detective Kate Lockley (future "Law & Order" regular Elisabeth Rohm), a police officer who would come to acquire substantial interest in the occult; Darla (Julie Benz), an evil vampire from Angel's past who appeared mostly in flashback; Lindsey McDonald (Christian Kane), an attorney with the evil law firm of Wolfram & Hart; Lilah Morgan (Stephanie Romanov), another W & H attorney; and Holland Manners (Sam Anderson), the nefarious W & H executive who oversaw the handling of Angel. Wolfram & Hart (and the unseen Senior Partners) would become the series's defining villain, represented through numerous attornies. The first season was mostly standalone episodes, with three crossovers with parent series "Buffy", and the series-length story arc involving Wolfram & Hart.
Season Two began where Season One had left off, with W & H resurrecting Darla and Gunn joing Angel Investigations. Darla, Angel's lover for 140 years, plays mindgames with her former flame. After she is turned back into a vampire (she was resurrected as a human), by none other than Drusilla (Juliet Landau), Angel goes dark and abandons the other members of his team, leaving them to carry on the fight by themselves. As Angel deals with Darla and Drusilla, the attornies at W & H continue their maneuvers, even as they experience considerable blowback from past operations. After the resolution of the Darla story arc, the series bid goodbye to Lindsey (for now) and Kate (for good), and then took a detour into the alternate dimension of Pylea. In Pylea, home of Lorne (Andy Hallet) [an ally introduced in the second season premiere], the gang meets the next addition to their cast, Winifred 'Fred' Burkle (Amy Acker). The end of the second season also marked a major change for the series, as its parent show departed the WB for another network, meaning that all future crossovers were nearly impossible. From thence forth, "Angel" must stand alone.
Season Three marked the show's descent into the darkness that would envelope it for the next two years, with things becoming somewhat brighter in the final year. Angel and Darla had had sex in Season Two, and, defying all known mystical rules, two vampires had conceived a child. That the child appeared to to be a major harbinger of destruction only made things more perplexing. Darla died in giving her son life, and Connor (as he was called) became the centre of his father's universe. But he also entered the radars of several powerful foes, notably Wolfram and Hart (now represented by Lilah, Gavin Park [Daniel Dae Kim] and Linwood Murrow [John Rubinstein]) and time-traveler Sahjahn (Jack Conley). Sahjahn, whom Connor was fated to kill, enlisted Daniel Holtz (Keith Szarabajka), an 18th Century vampire hunter with a massive vendetta against Angel and Darla. Meanwhile, Sahjahn's tampering with archaic prophecies caused a schism between Wesley and Angel. Holtz escaped with Connor to a demon dimension, even as Angel temporarily defeated Sahjahn. Meanwhile, Angel began to grow closer to Cordelia, and Gunn began a relationship with Fred. But a now teenaged Connor made his return from the demon dimension, stoked with a lifetime of horrific stories about his father. Connor's need for vengeance would culminate in the season finale, which saw Cordelia ascending to a higher plane, and Angel imprisoned deep in the ocean.
Season Four was the pivotal season of "Angel", where arcs that had spanned the entire series came into play. Even as Wesley rescued Angel from the ocean floor, a mysterious demonic foe know simply as The Beast (Vladimir Kulich) arose. After only a few episodes unseen on the higher plane, Cordelia appeared to return without much memory what had occurred; but the motives behind her return, and indeed behind the actions of the Powers (or specifically, one rogue Power) were much more insidious. The Beast was revealed to be a lacky of that rogue Power, who was using Cordelia to control her descent to Earth. After a brief arc that saw the returns of Angel's evil alter ego Angelus and vampire slayer Faith (Eliza Dushku), the Power was revealed as Jasmine (Gina Torres). Jasmine had orchestrated all the events leading up until that point, and now planned to bring her own strange peace to Earth that involved stripping mankind of free will and condemning them to banally happy lives. This season marked the death of Lilah, and ended with Cordelia leaving the main cast. After defeating Jasmine, Angel and Connor had one final confrontation, with Connor lost and reeling, and looking to die. Angel, desperate to help his son, struck a deal with the Senior Partners, whereby they gave Connor a new life and removed his memories of his past life, and also removed the memories of the rest of Angel's team; in exchange, Angel assumed control of the Los Angeles branch of Wolfram & Hart, becoming an employee of his mortal enemies.
Season Five saw massive changes to the show, with the gang now running Wolfram & Hart, and the addition of Spike (James Marsters) to the cast, replacing Cordelia. Spike, another "Buffy" transplant, became the series's second most important character, and he and Angel became the undead Starsky and Hutch; two souled vampires, two crusaders for good. Boreanaz and Marsters played off each other expertly, and the Angel/Spike rapport became one of the best features of Season Five. Season Five was the first season since Season One that seemed to lack a major plot arc, although a miniarc involving the return of Lindsey surfaced by the eighth episode. The series celebrated its one hundredth episode in Season Five, which featured the demise of Cordelia, and the defeat of Lindsey. But there was a major jolt coming, when Fred was consumed and replaced by an ancient demon named Illyria. Fred's death galvanized the series (as did the announcement that Season Five would be the final season), and the march towards the explosive series finale began. The series finale, Not Fade Away, featured Angel and co. going against he Senior Partners' chief servants on Earth, to demonstrate that they could not be controlled. The plan would in all likelihood mean their deaths, but the heroes had come to realize that the fight was what mattered. Wesley died in battle with sorcerer Cyvus Vail (Dennis Christopher), while the others completed their tasks; Lorne departed, the fight having become too bleak for his jovial soul. Angel, Spike, Gunn, and Illyria met up in a rainy alley, where the were confronted with the furious forces of Wolfram & Hart...and that was where the series ended, with Angel and his champions charging into battle, with their defeats all but assured; but the fight needed to be fought.