The Enchantress of Numbers (audio story)

 was the third story in the eighth series of The Fourth Doctor Adventures, produced by Big Finish Productions. It was written by Simon Barnard and Paul Morris and featured Tom Baker as the Fourth Doctor and Jane Slavin as Ann Kelso.

Publisher's summary
The TARDIS lands in the grounds of Newstead Abbey, Nottinghamshire, in 1850. Mistaken for a medic and his maid, the Doctor and Ann are brought to meet Ada Lovelace - the mother of computing and daughter of Lord Byron - who has recently fallen ill.

But the travellers are not here by chance. Something odd is happening on Earth, and they’ve determined that this place is the centre of it.

Strange figures are walking the land. Strange figures wearing bird-like masks. What do they want with Ada? And how will it change the future of humanity?

Part one
to be added

Part two
to be added

Cast

 * The Doctor - Tom Baker
 * Ann Kelso - Jane Slavin
 * Ada Lovelace - Finty Williams
 * Colonel Wildman - Andrew Havill
 * Hettie / Lady Cleverley - Eve Webster
 * Mr Hobhouse - Barnaby Edwards
 * Edvard Scheutz / Lord Byron / Harry - Glen McCready

Worldbuilding

 * Among elements "stolen" from history by the anti-virus are Charles Wheatstone, Wheatstones' residence at 168 Bleak Lane, the British Association for the Advancement of Science, and Albemarle Street, off Piccadilly, and the whole of Bloomsbury.
 * Edvard Scheutz is Charles Babbage's biggest rival. Since Babbage's retirement, Scheutz has been working on his calculation engine, which he feels is an improvement upon Babbage's analytical engine.
 * Scheutz has been acquiring Lovelace's private notebooks, stolen and sold to him by Hettie. The Doctor identifies recent pages' apparent "doodles" as Block Transfer Computations.
 * The anti-virus software, manifesting as plague doctors, were sent as a temporal expeditionary force from the year 7073, during the time of the Block Transfer Wars.
 * The Industrial Revolution took place recently, while the Computer Age is still "decades" away.

Continuity

 * The Doctor would met Ada again at an earlier point in her timeline in his thirteenth incarnation, but Ada's memories of that encounter were wiped. (TV: Spyfall)