In the beginning, Nicodemus was a street rat, no different from other rats, aside from a higher-than-average sensitivity to the Power. Towards the end of his life, he, along with several other rats, was captured on behalf of the scientific organization NIMH, and given injections which both prolonged his life, improved his mental capacity, and increased his latent psychic abilities.
Nicodemus was the first rat who discovered his ability to read, which he had picked up from the scientists' own mind thanks to his Powerfulness. This allowed him to understand instructions to open the door of his own cage. This allowed him to escape containment and free his comrades, rats and mice alike. He then deferred leadership of the escape operation to Jonathan Brisby, one of the Uplifted Mice he so freed. Along with the other rats, Nicodemus escaped NIMH through the building's ventilation system.
Setting up the Rosebush ColonyEdit
Nicodemus then led the Rats out of the city and through the wilderness, until they eventually arrived on Fitzgibbon's farm. There, he directed the creation of a subterranean lair under a rosebush, which would eventually become the Rosebush Colony. Due to his high intelligence, wisdom and power, as well as his role in the escape of the rats from NIMH, he was elected leader of the pack of rats.
With the help of other NIMH escapees such as Uplifted Mouse Mr Ages, Nicodemus used his newfound intelligence to create technological devices and reinvent science, progressively developping the Rats of NIMH as a true society rather than an unruly band of escapees. As a more personal project, Nicodemus also studied the Power to which he was sensitive since his prime youth, which he suspected was partly responsible for the process of Uplifting, as he had noticed that since the rats' arrival in the Fitzgibbon Farm, several lower animals had gone through changes that made them more humanlike and intelligent, some more than others. Most of all, he developped a bond with the Great Owl, a highly Power-sensitive animal whose wisdom almost rivaled that of the Uplifed rats, despite the other Rosebush Colons' insistance that this was sheer madness to interact so closely with a dangerous predator. During the same period, Nicodemus also took to writing a book where he wrote down his memories and his worries.
Thanks to his research, Nicodemus harvested the Power and his technological knowledge to create many devices, and chief among them, the Spinner. The Spinner allowed him to gaze upon any events he wished, although he was apparently limited to events the rats of NIMH themselves had witnessed, were witnessing or would witness. He used the Spinner to review past events of the Rats' history, scry upon the goings on of the area, and finally to gaze into the future, though he could only catch imprecise glimpses. He so predicted that a son of Jonathan Brisby would one day save the Rats from NIMH as his father had done before him.
Nicodemus understood that the Rosebush Colony lived on borrowed time; someday, somehow, humans would find them, unless they moved to a more remote region. He also thought, in his wisdom, that the now fully civilized rats had no justification to keep stealing their energy and food from the humans; he was of a mind that as long as the rats would live next to the Fitzgibbons's home, the temptation would be too great for them to resist. For those two reasons, he instigated a Plan to leave the Rosebush and create a new, larger colony in an uninhabited region, allowing them to live in daylight and produce their own goods. Despite the support of such prominent figures as chemist Mr Ages and Captain of the Guard Justin, Nicodemus's Plan was controversial at best among the Rats.
Creating the AmuletEdit
Nicodemus's extensive knowledge of the Power also allowed him to create an Amulet that would unlock a gigantic amount of Power to be used by the stone's owner, provided they showed 'True Courage of the Heart'. After creating the stone, Nicodemus became scared with its potential for misuse, especially fearing the consequences of the overambitious politician Jenner getting his hands on it. For that reason, he gave it to his trusted friend Jonathan Brisby for safekeeping. After the death of Jonathan at the hands of the Fitzgibbons' cat Dragon, the amulet was returned to Nicodemus, who had received instruction from Jonathan to give it to his wife, Mrs Brisby, in the event of his death.
Meeting Mrs BrisbyEdit
Nicodemus was torn between his will to fulfill the last wishes of Jonathan and his need to uphold the secrecy of the rats' origin. Due to this, he put off revealing the secret to Mrs Brisby, although he used the Spinner to keep a watchful eye on her, waiting for a chance to repay his debt to Jonathan. This chance came when her son, Timothy, caught pneumonia just before Moving Day. The Great Owl, whom Mrs Brisby consulted on this matter, sent her to the Rosebush. There, Nicodemus revealed the rats' history to her and gave her the Stone, along with a promise that the rats would move her house to the lee of a stone, keeping it safe from Fitzgibbon's plough. He also told her of the Plan, although only briefly.
As the Plan was finally underway, Jenner and his accomplice Sullivan decided to take advantage of the operation of moving the Brisby House into the protected area to murder Nicodemus, sabotaging the pulling mechanism to make his death appear accidental. Although Justin quickly unmasked Jenner afterwards, the plan was successfully executed and Nicodemus crushed under the rubble. Justin then took over leadership of the Rats and ordered immediate implementation of Nicodemus's Plan.
Differences with the NovelEdit
Nicodemus is also a main character in the original book by Robert O'Brian. However, he does not possess any Power-related abilities, including his iconic Spinner, as the Power itself is absent from the novels. Nicodemus's physical appearance in O'Brian's work is also notably different: he is much younger and more physically fit, has no beard or mustache, and wears an eyepatch. Due to Jenner's not being a murderous character in the book, Nicodemus also survives.