Professor Cairns was a Professor of Astronomy at the planetarium. She ends up accidentally involved in the "Case #4: Alex Woodbridge" segment of "The Great Game".
She gets involved when Alex Woodbridge contacts her when he starts to suspect that the lost Vermeer painting maybe fake. Alex contacts her when he spots that the "Van Buren supernova" in the painting even though it did not appear in the Earth's sky until years after the painting was meant to have been created.
Professor Cairns presumably believes he is onto something and starts to investigate the painting. She leaves a message on Alex Woodbridge's answering machine saying that he is right but it is unknown if they ever met up again as Alex was murdered by The Golem.
The Golem is hired to dispose of her, but is shadowed by Sherlock Holmes and John Watson. Whilst fiddling around with a recording machine in the planetarium, she is attacked by the Golem. Sherlock and John arrive, but Professor Cairns has already been killed.