I recently rewatched The Chase and The Time Meddler, and I really like Vicki.

Maureen O'Brien gives the little girl genius character — a role previously filled by Susan and in the future by Zoe and Adric — an air of maturity, mischief and irony.

In The Chase, when in the haunted house, she makes fun of Barbara for being afraid. She impersonates the Mechanoids, which Barbara finds inappropriate. And she explains the TARDIS to Steven with a wry smile on her face.

And the irony. Look at Maureen O'Brien’s facial expressions. (And she has quite a deep voice; deeper than you would imagine for a girl with pigtails.)

“Zero.”

Zero, I assume, is Mechonoid-speak for sod off.

OMG the Mechonoids are so cute, though.