A tall, handsome man with white hair, strong features and intense eyes, Slade was brilliant, but arrogant and devious. Morris Blackletter, a former Longitude consultant, described him as "evil" and said he had a way of pulling good people into his maelstrom, while another former colleague recalled Slade being "an amazing combination of visionary brilliance and extraordinary caring - mingled with unbelievable greed, even cruelty." It was said all of Longitude's employees lived in fear of Slade, except his executive secretary June Brodie.
Slade personally headed Project Aves, a secret group within Longitude that sought to create a mind-enhancing drug from a mutant strain of avian flu for the Covenant. Slade continued experimenting with the virus even as Longitude was going bankrupt. The project began cutting corners and ignoring safety protocols, until a parrot infected with the virus escaped and infected a family in a nearby town. Slade knew about the escape and decided to let the unplanned "experiment" run its course. The family was driven insane by the virus and individually came to horrible ends.
Slade was apparently killed in a fire that broke out in Complex Six, the laboratory where Project Aves experiments were conducted. Shortly afterwards, Longitude filed for bankruptcy and June Brodie disappeared, an apparent suicide.
Special Agent Pendergast and Captain Laura Hayward located a still-living Charles Slade at Spanish Island in the Black Brake Swamp. After faking his death, Slade had retreated there with June Brodie and her husband Carlton to continue their research far from the oversight of government regulatory agencies and the Covenant. Slade had become infected with the avian flu and for a time had greatly increased mental faculties. He conducted experiments and cured June Brodie's amyotrophic lateral sclerosis (Lou Gehrig's disease), although - despite the pleadings of the Brodies - he kept no written records of his research or findings. As the disease ravaged him, he became insane and hypersensitive to external stimuli.
By the time Pendergast and Hayward found him, Slade was confined to a few small rooms in his Spanish Island lab. He was gaunt, edgy and addicted to morphine, carrying a short leather whip which he used to flail himself as a counterirritant when the sensory overload became too much to bear.
Pendergast confronted Slade, who freely admitted his involvement in Helen's death, willfully - defiantly, even - leaving out the involvement of Pendergast's brother-in-law, Judson Esterhazy, and the company's link to the Covenant. Pendergast, who had promised not to kill the former CEO, suddenly handed his gun to Slade, who promptly aimed it directly back at the FBI agent. As Slade was about to shoot, Pendergast asked to speak to him alone. Once inside Slade's office, Pendergast wound a cuckoo clock and spoke to Slade, describing the torment of life with Slade's condition and forcing him to face the truth: the disease was incurable, and Brodie was keeping him alive in vain hopes. As Slade struggled with the revelations, the agent lit a packet of activated charcoal to produce smoke, described the sensations of eating and drinking and reminded Slade that he hadn't enjoyed a meal in years. As the clock struck twelve, Slade, unable to bear the agony of so much sensory input, turned the gun on himself and pulled the trigger.