Retirement can be boring, but not so for Reuben’s Gramps! In the time he now has to spare, this retired professor of neuroscience sets about to build a machine that can amazingly be programmed to change people’s behaviour! To make Reuben believe in the machine, Gramps tries it out on a pompous next-door neighbour. Apart from a few glitches, the machine seems to work successfully. Gramps treats Reuben and his best friend Simon and local, accident-prone gardener Bert, (known in the village as Blundergutts), to a day out in London to experiment more with the machine. 
In Victoria Station, they see Ted, an unpopular man from their village, is on his way to play the cymbals, for the first time, in a concert. Gramps uses this unexpected opportunity to interfere with Ted’s performance by causing him to clash the cymbals at the wrong moment, to disrupt the concert and turn proud Ted into an absolute failure. Reuben and Simon are always picked on at school by Mr. Pride, their horrible headteacher. During a government inspection at their school, Reuben 'borrows' Gramps' spare machine and creates absolute chaos, causing the immediate suspension of Mr. Pride. 
Is there a limit to the amazing mind machine - or should there be?! Find out as Reuben and co test their limits and discover what a mind machine can really do!