Gameplay is built around the "walk and talk" mechanic: instead of dialogue occurring during cutscenes, speech bubbles appear over Alex's head, giving the player a choice between two or three dialogue options. At the same time, Alex remains free to move around and navigate the game world. Players can select dialogue options at any time during conversations, choosing to wait for other characters to finish, to interrupt, or to remain silent. Certain dialogue options cause a thought bubble with Alex inside it to appear over characters' heads, suggesting that the player's choice had an effect on the characters' relationship.
Objects that can be interacted with in the game world display a small circle next to them. Puzzles in the game are solved by finding the correct frequency on Alex's handheld radio, which can perform actions such as unlocking doors or communicating with ghosts, or by winding up tape recorders at the correct speed. Oxenfree does not have any "game over" loss conditions; the player's choices and relationships with the characters determine which of several possible endings the player receives.
Plot
Alex (Erin Yvette), a teenager, is on the last ferry heading to the fictional Edwards Island for a weekend party. She is accompanied by Ren (Aaron Kuban), her stoner friend, and Jonas (Gavin Hammon), her new stepbrother. On the island, Alex and company meet Clarissa (Avital Ash), ex-girlfriend of Alex's deceased brother Michael, and Nona (Brittani Johnson), Clarissa's best friend and Ren's love interest. Ren explains the island was once a military base and that the island's only permanent resident, Maggie Adler, has recently died. After camping on the beach, Alex, Ren, and Jonas explore the nearby caves, where it is rumored certain radio frequencies cause supernatural events. In a small cavern, Alex tunes her radio and unexpectedly forms a dimensional rift. A voice answers and the teens experience visions before passing out. Jonas and Alex awake in front of a communications tower elsewhere on the island. Ren calls, having passed out in the woods, while Clarissa calls from the decommissioned military fort on the island.
In the woods, Jonas and Alex encounter supernatural events, including Alex's reflection in the water communicating with her, objects moving on their own, and time looping repeatedly. Time corrects when Alex plays a reel-to-reel tape. They spot Nona, who claims she saw an alternate Jonas and Alex. Alex and Jonas find Ren, but after another time loop, they find him possessed by a "ghost". Using the radio, Alex creates another rift which returns Ren to normal. Ren and Nona return to the tower.
At the military fort, Alex's reflection appears in a mirror, giving Alex advice. A ghost questions them and possesses Jonas, revealing that the ghosts are the passengers of the submarine USS Kanaloa, thought lost at sea. Alex creates another rift that revives Jonas. They find Clarissa, but time loops to her jumping to her death before disappearing. Nona, Alex, Jonas, and Ren regroup at Harden Tower. Unable to send a radio transmission off the island, Ren suggests finding the key to Maggie Adler's estate, where she kept a boat. At Adler's estate, a possessed Clarissa talks with Ren; her conversations and scattered letters left behind by Maggie Adler reveal that Adler mistakenly interpreted scrambled messages from Kanaloa as an enemy transmission, and the submarine was sunk by friendly fire. The crew was not killed, but transported to another dimension due to the sub's experimental nuclear reactor. Adler and her friend Anna attempted to communicate with the Kanaloa crew via a radio, but Anna was absorbed through the rift. The Kanaloa crew intend on using Alex and her friends' bodies to escape the dimension, keeping them on the island long enough for their possession attempts to be successful.
Alex and the group discover Maggie Adler's plan to fix the rifts—crossing to the other side of them and tuning the radio within. Alex repeatedly loops back to the past, mainly to times she talked with Michael. A ghost possesses Jonas and attempts to bargain with Alex, offering to spare her and the rest of her friends if they leave Clarissa behind. Returning to the caves, Alex tunes into a rift that sends her into a void. Encountering the possessed Clarissa, the ghosts warn Alex that she will die if the rift is closed, and Clarissa will be kept by the ghosts if Alex leaves through the rift. Alex can choose to leave, erasing Clarissa from existence; close the rift herself, trapping her with the ghosts; or, if she has found enough letters from Maggie Adler, Alex can appeal to the crew members directly, convincing them to let Clarissa and her go. The reflection of Alex giving her advice is revealed to be Alex from the future. She loops back to a conversation with Michael, who admits that he and Clarissa are planning to move away from town and asks for Alex's advice. Time then corrects.
Alex wakes up with the others on the ferry back home; Jonas informs her that whatever she did fixed the rift and that everything is normal. Everyone reveals that, for a limited period, they revisited past memories. They then swear to not tell anyone about their experiences. Nona takes a final group picture.
