M is for... Mona Lisa

In the early years of the 16th Century, the polymath Leonardo Da Vinci painted a work which came to be known as La Gioconda. It was the portrait of a woman with an enigmatic smile, and under its more common title - the Mona Lisa - it would become the most famous painting in the world.

However, the ruthless Captain Tancredi commissioned him to paint a further seven copies of the work, which were to be stored in a bricked-up basement room in a Paris townhouse.

Tancredi was really an alien - Scaroth, last of the belligerent Jagaroth race. His ship had exploded on prehistoric Earth, causing him to be splintered through the planet's history up to the late 20th Century.

In order to fund experiments which would result in a working time machine capable of taking him back to prevent the blast, he amassed many rare works of art. The seven copies of the Mona Lisa were in his home.

In his latest guise as Count Scarlioni he would arrange for eight buyers - all unknown to each other - to purchase the painting after it had been stolen by his gang from the Louvre. Each would think they were getting the stolen picture, allowing him to sell it eight times over.

Unknown to him, the Doctor travelled back to Florence in 1505 and had written "This is a Fake" in felt-tip pen on each canvas, which would show up in X-rays. The Count's home burned down after his time machine was destroyed, leaving only one of the "Fake" versions to go back to the art gallery.

30 years later, the painting was loaned to the International Gallery in London, where it was visited by Luke Smith, Clyde Langer and Rani Chandra. They were on a school trip, the result of an art competition won by Clyde. 

It transpired that Leonardo had borrowed pigments from an artist neighbour - the eccentric Giuseppe di Cattivo - who had used them to paint a monstrous creature. This work was known as The Abomination, and it was held in the gallery's vaults - too frightening to be exhibited.

The pigments had been ground from a sentient piece of rock which had fallen from space.

Brought into close proximity, the Mona Lisa came to life and emerged from the painting. She was determined to reunite with her "brother" from di Cattivo's painting. Able to bring other artworks to life, she armed herself with a Sontaran blaster - taken from Clyde's winning picture. She could also place people inside paintings - as happened to Sarah Jane Smith when she came to investigate the events at the gallery. One thing she could not do, however, was leave the confines of the gallery - otherwise she was reduced to lifeless pigment.

When K-9 destroyed the emerging Abomination, the Mona Lisa was converted back into a painting - though one with a consciousness trapped within it.

Played by: Suranne Jones. Appearances: City of Death (1979), SJA 3.5 Mona Lisa's Revenge (2009).

• Jones would later play Idris, the soul of the TARDIS, in The Doctor's Wife.
• In order to pad out The Final Problem, which closed Jeremy Brett's first series as Sherlock Holmes, writer John Hawkesworth borrowed the Mona Lisa plot from City of Death - with Moriarty now trying to sell multiple copies of the painting after stealing the one from the Louvre, though naturally his are simply forgeries.