While patrolling LA, brand new Slayer Buffy finds an amulet and sticks it in her jewelry box to deal with later. Upon moving to Sunnydale, the amulet gets dropped as Buffy is moving into her new room and Spike pops out of it. Spike is a ghost and can only interact with the owner of the amulet, Buffy. He is bound within 50ft of her and cannot be seen, heard, or touched by anyone else. 

Though they struggle at first with sharing space, their mutual need for companionship draws them together. Eventually, the two make it their goal to recorporealize Spike. 

Spike's ghostly presence changes Buffy's first year in Sunnydale. He warns Buffy that Angel is a vampire. When Spike gets dragged to school with Buffy, he gets exasperated at her apparent lack of book smarts and feeds her answers. Spike also has no trouble pointing out to her in the rudest way possible when she makes a mistake on patrol. Unfortunately, his presence also makes it more difficult for Buffy to make friends and her mom is worried about how much she talks to herself. It also doesn't help that Buffy starts getting lusty feelings for a guy who can't take her on a date.

The amulet, obviously, is the one from Wolfram & Hart. How did Spike get trapped? Why? And more importantly, do they want him back? While this definitely has a romance-y character driven hook, there is a lot of room for serious plot and action. If Wolfram & Hart trapped Spike, they could come looking for their amulet and meet a very determined Slayer.