After being on board a short time, Jameson seems much stronger to his wife, but then is wracked with pain. He claims it's nothing-"just body changes" that he was warned to expect. However, Beverly finds his medical records are two months out of date, and Jameson later shocks the bridge by getting up out of his support chair (something which he should never have been able to do) to take the Con.
After Jameson starts looking younger and is then again seized by pain, his wife Ann calls Dr. Crusher for help. Picard questions Jameson and discovers what has happened: Jameson, not long ago, went to Cerebus II to obtain a process that gives one one's youth back. He was taking it gradually for months, but then, when this crisis surfaced, he not only took all of his own dosage at once, but all of the dosage he'd obtained for Ann as well. A short time later, Jameson opens a secret channel to Karnas, where he discovers that there are no terrorists: Karnas is holding the hostages himself, and wants Jameson for some as yet unspecified revenge.
After Jameson orders the ship to accelerate for an early arrival at Mordan, Picard talks to him privately. (By this time, Jameson is physically in his mid- to late-twenties.) He hears the truth of what happened 45 years ago: rather than negotiating to free hostages Karnas took then, Jameson gave Karnas the weapons he wanted, but also gave them to his enemies, inadvertently causing forty years of civil war.
Arriving at Mordan, Jameson leads an armed rescue mission, which is aborted when he is again hit by another spasm. Karnas hails the Enterprise, demanding Jameson in ten minutes' time. Jameson, dying, beams down and eventually manages to convince Karnas that he is in fact Mark Jameson. His cells imploding, Jameson then dies in excruciating pain. Karnas, cheated even of his revenge, frees the hostages and agrees to bury Jameson's body on Mordan. The Enterprise, saddened by their loss, departs.