Jackson Lake Jackson Lake was a 19th century mathematics teacher who briefly believed himself to be an incarnation of the Doctor , but in reality , had his memories altered by a Cyberman infostamp . As the real Doctor told him , the Infostamp that backfired , and made him believe he was the Doctor , only gave him information about the Doctor ; all the bravery and his invention of a different kind of TARDIS , were things he was capable of doing on his own . Biography . Lake was a mathematics teacher . In 1851 , he moved to London with his wife , Caroline , and son , Frederic . They soon encountered the Cybermen , who killed Caroline and abducted Frederick . 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 cracked . He entered a fugue state in which he believed he was the latest incarnation of the Doctor , newly regenerated and amnesiac due to the Cyberman attack . Some time after this , he rescued a woman named Rosita from a " man made of metal . " Dubbing her his companion , he began to work on his own " Tethered Aerial Release Developed In Style , " or TARDIS . Lake continued to act as the Doctor would , investigating the " disappearance " of a man named Jackson Lake as well as the kidnapping of local children . His exploits soon bought him into contact with the actual Doctor . At first , the real Tenth Doctor believed Lake to be his own future incarnation , but began to suspect that the man was not who he claimed to be when Lake attempted to use an ordinary screwdriver to ward off an attacking Cybershade . After uncovering enough evidence , he deduce d Lake ' s true identity , and revealed it to him . With the sudden knowledge that he was not who he thought he was , Lake had a breakdown and told 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 most 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 , Rosita , and the Doctor fought their way under the River Thames . There the kidnapped children were used as slave labour , 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 had taken from him - his son . Finding his son in the factory , but too paralysed with fear to save him , Lake marvelled as the Doctor leaped into action and rescued the boy . He watched from the streets 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 . With Lake now a widower looking after a young son , there was no question of the Doctor inviting Lake to join him in his travels . Still , Lake begged for a look inside the TARDIS , to which the Doctor agreed . Overcome by the unbelievable , Lake forced himself to exit , ecstatic to have finally seen the ship but quite through with adventure . Reunited with his son , and appointing Rosita as his nanny , he invited the Doctor to a Christmas dinner , an offer that the Doctor refused , even when Lake suggested it be " in honour of those we have lost " . However , when Jackson insisted , the Doctor finally accepted , happily . ( TV : " The Next Doctor " ) Personality . 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 true bravery deep within himself . The Doctor informed Lake that this was his own doing , not an effect of the infostamp . Even after his true identity reasserted itself , Lake retained much of the knowledge he had obtained through his brief experience as the Doctor , although he found it hard to accept the reality of the Doctor ' s TARDIS . ( TV : " The Next Doctor " ) Other information . Jackson Lake carried his own version of a sonic screwdriver which was , in fact , an ordinary screwdriver . When asked how it was " sonic , " he said it made a sound , demonstrated by tapping it against a doorframe . He also carried a fob watch . The Doctor initially suspected this to be a Chameleon Arch biodata module , but discovered otherwise when he opened it and found only a normal watch face . The watch did contain the secret of Lake ' s true identity ; his initials were engraved on the back . ( TV : " The Next Doctor " )