Woody's father, an obstetrician, asks his son and the rest of Mr. T's gymnastics team to investigate the mysterious deaths of children in Williamsburg, Woody's hometown. Who could be responsible? All they know is that the children were poisoned.
In the introduction sequence, Woody Daniels tells some kids, who are close to giving up after one of them lost his wallet and they cannot find it, that giving up when something proves too hard is not the right thing to do and that with perseverance, they can do what they are trying to do. To bring his point across, he starts to tell the story of The Mysterious Poison.
The story starts in Williamsburg where Mr. T and the team are visiting Woody's parents in Williamsburg. Woody's father is an obstetrician whose job is to deliver babies. While showing the team the hospital, Woody's father is contacted by one of his assistants. 12 newborn babies have died mysteriously. The team asks to investigate. Woody's parents agree. The first thing to do is to get the coroner to perform an autopsy. What they is that the babies were poisoned. It is clear that they have been murdered. The team investigates further, but more babies continue to die at the hospital. Woody is worried that his father will be out of a job as fewer mothers are now coming to the hospital to give birth. To make matters worse, the investigation is going nowhere. When the twenty-fifth baby dies, however, they find the card of Woody's father's boss, Dr. Fitzpatrick. They question him, but he denies any involvement. Robin does not believe him. While rummaging through the FBI files on her laptop computer, Kim discovers that Dr. Fitzpatrick is under FBI investigation. Things get out of hand when Spike is attacked in his hotel room by a mysterious assailant. Jeff manages to drive the man off. Spike is okay. Mr. T calls the police, and they catch Dr. Fitzpatrick as he is about to poison another child. He is arrested. A search of Dr. Fitzpatrick's house reveals that he is a pedophile and a serial killer of children.
In the concluding sequence, Woody explains that it took perseverance to capture Dr. Fitzpatrick. He explains that with perseverance, they can find the missing wallet. Sure enough, the kids find it. Woody congratulates them. He then turns toward the audience's and tells the audience that if they are having trouble doing something, they shouldn't give up. Perseverance will help them in the end.