This is now one of three Who Was Here caches I have hidden in the local area, the other two being Who Was Here 25: Spearhead From Space, in Radford, Worcestershire, and Who Was Here 24: The Krotons, in Malvern, Worcestershire.
The Girl In The Fireplace was a 2006 Tenth Doctor story. The given co-ordinates are for Ragley Hall, where the ballroom scenes in the story were filmed.
The cache is of course not hidden at the given co-ordinates or on the grounds of Ragley Hall. Instead, I have hidden the cache on one of the roads that surround the grounds and therefore should be a quick cache and dash.
However, to locate the cache you must solve the following -
The Girl In The Fireplace is a famous French historical figure. Find out who she is and more importantly, discover her date of birth (DD/MM/YYYY=AB/CD/EFGH) and the date she died (DD/MM/YYYY=JK/LM/NOPQ).
The cache is hidden at N52 CD. KGM W001. KQ. AAK