He was a mathematics teacher. In 1851, he moved to Victorian London with his wife and son. They soon encountered the Cybermen, which lead to the death of his wife, and apparently his son. He somehow used an Infostamp to defend himself, but the device backfired, filling his mind with information the Cybermen had gathered on The Doctor. In his anguish over the loss of his family, his mind fooled itself into believing that he was actually the latest incarnation of The Doctor, newly regenerated, and amnesiatic, due to the Cyberman attack.
Assuming the identity of the Doctor, Lake continued to act as his namesake would, investigating the "disappearance" of a man named Jackson Lake (unaware that he himself was Lake), as well as the kidnapping of many local children. His exploits soon bought him into contact with the actual Doctor. At first, the real Doctor believed Lake to be his own future incarnation, but began to suspect that the man was not who he claimed to be. After discovering enough evidence, he deduced Lake's true identity, and revealed it to him. Left aghast, Lake allowed Rosita to accompany the real Doctor as he confronted Mercy Hartigan.
The Doctor and Rosita discovered the location of the kidnapped children, as Lake struggled with the devastating truth. Having recovered his memory, but unable to remember what the Cybermen "took" from him, he found the courage to join Rosita and the Doctor, arming himself with a bandolier full of Infostamps. Using the devices to attack the Cybermen, Lake was able to fight his way under the River Thames, where the kidnapped children were used as slave labor, forced to construct the CyberKing Dreadnought, a massive weapon and Cyber-conversion factory, created for the invasion of Earth. As The Doctor and Rosita evacuated the rescued children, Lake recovered his memory completely, remembering what the Cybermen "took" from him - his son.
Finding his son in the factory, but too paralyzed with fear to save him, Lake marveled as The Doctor leaped into action and rescued the boy. He watched as the Doctor took the hot-air balloon to confront Hartigan, and end the Cyber threat. Having shared memories of the Doctor from the Infostamp, he knew that the Doctor was rarely ever thanked for his exploits, and so, he rallied the assembled masses to cheer for, and thank the Doctor.
The crisis averted, Lake and the Doctor met near the TARDIS. Lake begged for a look inside, to which the Doctor gladly agreed. Overcome by the unbelievable, Lake forced himself to exit, ecstatic to have finally seen the ship. Reunited with his son, and appointing Rosita as his nanny, he then invited the Doctor to a Christmas dinner, an offer that was at first rebuked, but finally accepted.
- At first, Lake was a somewhat shy, average man. Due to the effect of the Infostamp, and under the belief that he was The Doctor, Lake became a brave, dashing hero.
- Once his memories as Jackson Lake returned, his confidence waned, but as the threat of the Cybermen loomed, he discovered a true bravery deep within himself. The Doctor would later inform Lake that this was his own doing, not an effect of the Infostamp.
- "I'm the Doctor! Simply the Doctor! The one, the only... the best!"
- "This is a job for a Time Lord!"
- "Are you whistling again?"
- Jackson Lake carried his own Sonic Screwdriver. However, this was merely a normal screwdriver. When asked how it was "sonic," he informed The Doctor that it does indeed make a sound, demonstrated by tapping it against a doorjamb.
- Lake also carried a fob watch. The Doctor suspected this to be a Chameleon Arch fob watch, but discovered that it wasn't. Still, the watch did contain the truth to "The Next Doctor's" identity - Jackson Lake's initials were engraved on the back.