Oak gets pulled into Barovia before the Dungeon Rats do, and ends up stealing a letter from a party of Outsiders that he failed to join up with. Meeting with Strahd alone, Strahd realizes how easily manipulated Oak is, and uses this to his advantage, asking Oak for help protecting him from the whims of those who seek to spell out his downfall. Oak, eager to find purpose again, accepts.
Oak helps deal with the adventurers, pulling them into trials set up by Strahd, essentially meaning that Strahd is having fun with the adventurers without having Oak get his hands dirty. Everything Strahd asks of Oak at first is easily within Oak's range of abilities, and Strahd rewards Oak heavily for his help, essentially ensuring that Oak is endearing himself to Strahd.
Eventually, Strahd starts asking more and more of Oak, to which Oak happily obliges. Eventually, Strahd asks Oak to join in with a party of Outsiders and lead them into Strahd's plans. Oak obliges, and feels a little bit of remorse deep in his stomach while he does so. After the party is dealt with, Strahd tells Oak that he is doing a wonderful job, and that he is not like the other Ousiders. The party had grown on Oak a little bit as he got to know them, and there is that seed of doubt planted in Oak that Strahd is entirely as he seems on the surface. But Strahd is good to him, and after everything that had happened with Connor outside of the Mists, that is all Oak needs to refuse to give that doubt purchase in himself.
This happens a few times, and Oak doesn't allow himself to get close to another party of Outsiders. Until the Dungeon Rats come into the Mists. Oak bonds with them quickly, and they are happy to have him! Oak feels the guilt in his stomach surge again, as he tries to ignore what he knows will happen to this party at his own hands. Strahd is able to see how Oak feels about this party, and allows Oak to travel with them fully, and not to pull them into some of his usual traps. Even when Strahd appears to begin to break up the party, he sees how Oak is acting and changes his plans accordingly, as this is new and interesting behavior from the halfling that has been following his every order unquestionably up to this point in time.
The Dungeon Rats are semi-responsible for disaster that is the Festival of the Blazing Sun, in which the Burgomeister of Vallaki and his wife die tragically at the hands of the Brides of Strahd. They attack the Rats viciously, as what Oak thinks is part of Strahd's challanges. In reality, they are taking this chance to have a free shot at Strahd's newest plaything without drawing the direct ire of the Vampire Lord. Unbeknowest to Oak, Strahd deals with one of his Brides after they threaten life of the current iteration of Tatyana.
The Rats travel to the Amber Temple, in which Oak takes a pact with Vaund the Evasive, unknowingly obscuring his every move from Strahd. Strahd, not seeing Oak as a threat at all, is excited by this advancement, because it means he has an underling that is undetectable by all that would oppose him.
Eventally, the Rats become strong enough to approach Castle Ravenloft, where Strahd greets them, and dines with them before their challange against him. He acts cordial to them, and continues to play the victim, not fooling any of the party members except for Oak.
The party ventures through the castle, eventually reaching the catacombs. As the explore parts of the castle that Oak hasn't seen before, he is met by one of the tombs that displays his name on the front. The scene unsettles the party, but grants a weird sense of reassurance to Oak. After all, many of the people that Strahd loved and respected were entombed here. Oak doesn't realize that Strahd has a pechant for sealing away those who he has grown bored with. Later this fact will also read as a threat to Oak.
It is in the Tomb of his brother that they find, and ultimately challenge Strahd. He plays on their emotions one final time, before rising to challenge them. Every shot Oak takes at Strahd misses, to which Oak is thankful. It also serves to show Oak that maybe, just maybe, Strahd doesn't actually need Oak's help in dealing with those that stand against him. For a moment, Oak is fighting with the same intensity as the rest of his true party. With the same frusturation. With the same hope. And then one of his party members casts a lightning bolt at Strahd. And Oak's alliance shifts away from the party as he becomes frightened of the party member. He spends the rest of the fight hiding from the party, until the Bearer of the Sunsword has all but cornered Strahd. From his spot behind Sergei's tomb, Oak lines up the shot in a moment of despiration, and his aim rings true. A crossbow bolt lodges itself in the forearm of the Sunsword's weilder, and the Sunswrod topples from her grasp. In a moment that lasts forever, she meets Oak's gaze. Confusion and betrayal radiate outward from her, as Strahd sinks his teeth into her neck.
The rest of the party falls soon after. Oak is shellshocked. Strahd thanks him for his help, and Oak doesn't reply. Strahd summons his unseen servants to clean up his brother's tomb, and as they begin to move the bodies of the fallen, Oak finds his voice. He shakily asks Strahd if the party could remain as they were. Strahd dislikes this moment of weakness on his underling's part, but instructs the halfling on how to prevent the dead from coming back. Snidely, he tosses Oak the Sunsword, and tells him that if he wanted to finish the party's job, now would be his best chance. Oak falters. In a better world, perhaps, Oak killed Strahd here. But the Sunsword refused to activate for him. It saw firsthand what he did. Oak doesn't meet Strahd's gaze, and Strahd dismisses Oak.
With the help of Bucephalus, Oak is able to transport the fallen to a spot in the Svalch Woods, just outside of the Village of Barovia. It is there he seeks out Shari, lying to her about his circumstances. She takes pity on him, seeing her situation in his, and casts a ceremony spell over the dead. Shari talks to Oak, and asks him what he plans to do with their bodies, gently letting him know that there are things in the woods that would disturb their rest. After all, Ceremony doesn't dissuade animals from an easy meal. Oak nods, and asks Shari if she would watch over him as he dug their graves. She agrees, but informs Oak that she will not be much help in defending. In a parallel to an event that Oak would know nothing about, Oak buries his friends, and lays the Sunsword to rest with its weilder. It protests, and a powerful wave of emotions washes over Oak. He crumples to the ground, almost pitching into the open grave. Shari shouts, and rushes to grab him. Oak fully passes out.
He comes to an hour later with Shari looking over him in worry. She tells him he is doing too much too soon, and advises him to rest. He refuses, as he has a duty to his friends to finish. Soon, all that remains of Oak's party is upturned dirt. Shari offers Oak a place to stay in the village, at least for the night, and Oak refuses again, telling Shari that he wants to make sure that his friends don't come back. Shari nods, and leaves Oak by himself. When she returns in the morning, Oak is gone. Shari finds [something??] on the altar of the temple when she returns, a small thank you from the other halfling. [shari and oak meeting at other times? oak visiting the gravesite occasionally--protected by a hallow spell, the sunsword and its bearer bones have risen to the surface. oak doesn't move the sword. one day it is just gone, and Oak carefully places a haleberd in its place.]
Strahd is somewhat surprised to see Oak return to his side willingly. He is easy on Oak for some time, before doubling down, giving Oak harder and harder tasks to complete in his name, including directly turning on other parties of Outsiders after befrending them. At one point, Oak acts out, trying to warn the party of what is to come. Strahd tears that party apart, bit-by-bit, not granting them the mercy of a swift death, and Oak says nothing. He does what Strahd asks, and is rewarded for doing so.
As Strahd grows crueler towards Oak, Oak begins to walk a dangerous line, obeying and almost trying to predict Strahd's whims to stay on his good side, but also doing what he can to spare the Outsiders a cruel death at Strahd's hands. All goes as well as it can, until Strahd finds Oak standing over an Outsider that Strahd had been showing an interest in. Strahd throws Oak into Oak's named crypt, and leaves him there. Oak exhausts his limited supplies while in there, unable to escape. He rationalizes Strahd's actions, giving himself a false sense of security as he lays atop his cold slab. And Strahd does come back for him.
Once again, Oak is loyal to every whim of Strahd's. He ignores it when Strahd's Brides stop harassing him, and takes it as if they have learned that he is a part of the Castle that will not be leaving. And then one day, Strahd calls Oak alone into his [throne room? the one that oak saw him in but snuck out of in the actual campaign], where he praises Oak for all that he has done. Oak is filled with a false sense of security, as he willingly fails to Strahd's charm. But something he had forgotten, a shard of amber buried deep in his soul from days long past, screams out at him. And Oak comes to, with a chilling realization that Strahd wasn't holding him like he once would. Oak cries out, trying to find some way to push Strahd away, but he can't. Oak knows this is it. His movements grow less frantic as the edges of his vision begin to fade out. And he makes a desperate plea for something, anything, to save him.
And something does hear him.The amber shard in Oak’s soul resonates, and Oak’s bond with Vaund the Evasive, forged years ago, deepens. Oak becomes incorporeal in Strahd’s grasp, and drops to the floor, before quickly backing away from Strahd. Oak sees something glint in Strahd’s eyes as he wipes Oak’s blood off of his mouth. Oak shivers, feeling the bite left on his neck. He can’t move, as if frozen in place by Strahd’s gaze. Unbeknownst to Oak, his outline begins to flicker. In a moment, Strahd is seemingly alone. Banking on the fact that Oak still hasn’t moved, Strahd keeps his gaze level, and tells the halfling to “Consider that a warning, Oak'lahoma,” before turning his back and walking out of the room.
Almost a half hour passes before Oak is shaken out of his stupor. He runs from the castle, and doesn’t stop until he is just outside the Village of Barovia. On autopilot, he ends up at the location where he buried the rest of his party. Oak hits the ground, clutching his chest--he can’t catch his breath, and his body feels like it is fighting him at every step as the adrenaline wears off. Struggling to stay conscious,Oak ends up on his side, and the last thing he sees is the skeleton, half-buried, of the former bearer of the Sunsword.
Shari finds Oak in the morning. She had taken to visiting the site, recognizing it as Hallowed ground, safe from the tampering of the undead. Upon seeing Oak, collapsed and covered in his own blood, Shari freezes. Oak must have been alive when he arrived, but Shari is unable to see his chest move. Fearing the worst, she hesitantly reaches out to touch him--and as her fingers brush his shoulder, Oak jumps back to life. Shari falls backwards, and before she knows it Oak has put distance between them and drawn his dagger. Shari raises her hands in a gesture of surrender, and oak’s blade falters in his hand. He lets it fall through his fingers, and the tip of the blade sinks into the soft ground.
Shari and Oak talk. All oak shares with Shari is that he was attacked, and that he barely escaped. Shari remembers what happened to her and her party, and sees herself in Oak. The rest of the conversation is one-sided. Shari fills the space between them with empty reassurances and false hopes that they both have the misfortune of seeing straight through. After some time, Oak tells shari that they would likely not meet again, to which Shari tries to protest. But when they meet each other's eyes, shari knows deep down that it is for the best. Shari is the first to leave, and when she looks back, the other halfling is gone.
Oak avoids drawing the ire of Strahd by virtue of staying out of his sight, all while doing his best to continue to obey strahd's commands. He becomes more familiar with his abilities, and begins to use them to his benefit. In doing so, he becomes bolder, eventually working up the courage to meet Strahd face to face once more.