Overdose is an action-packed, survival horror, free-roaming game. You'll play as Craig Markson, a veterinarian and father of Sheila Markson. With GTA-style gameplay as you explore Hambver Town in search of Sheila, his girlfriend: Madison Dalvin, his supposed to be deceased wife, a cure and his connections to the tragedy. Although the game plays like a classic horror game with pre-set camera angles.
In the small town of Hambver, most of the the townsfolk have cancer. One day, the infamous Retmotech Labs introduced their concoction of what they call Cancer Pills. With just one dose, it can cure cancer within a month. But one persistent person who has cancer and will die within less than a week overdosed himself with the pills thinking it will speed up the effects. But later that evening, the teenager died. Blood started coming from his mouth and he mutated. Arms grew out of his back with large amounts of blood pouring out. He attacked everyone in the house. It was raining. Dr.Craig Markson was treating a dog who was bitten by his "deranged" owner who was taken to the town's asylum. The dog started acting weird in his cage and he asked his assistant and best friend, Nolan Wesche to watch the animals. Meanwhile, in Sheila's school, an cave-in occurs during class and Sheila is stuck under debris. She witnesses creatures emerging and she screamed. Then we turn to Dalvin Memorial Library, where Craig's girlfriend, Madison Delvin works. She is looking after a sick person who escaped from the asylum and attacked his dog. He tells her that "everyone will die". Suddenly, his jaws rip apart and then the man tries to bite Madison with his huge mouth. Then it switches back to Craig as he walks downtown in his break. It starts to rain. He sees news reports and sees news reports of unidentified creatures near the town's volcano. Suddenly, an "earthquake" occurred and a worm-like creature appeared at town square and sprayed black mist into the clouds. Everyone was knocked out. Craig awakens alone in town. It was nighttime but Craig looked at his watch and saw it was only 10:00 AM. He tried to go back to his apartment. On his way there, he came across an open manhole. He heard screams and entered the manhole bravely.