Could it have been Emperor Red with the Lanyard on the stairs ?
To find the cache you will need to find the numbers from the other caches in the series. Links can be found below.
Here is a starter for you N51.AB.--- E000.CD.---
Have fun, happy caching.
Here are the caches in the series.
PUZZLE BONUS.
Click GC3YKFC to visit Cludo Who Dunit?
TRADITIONALS.
Click GC4BEPM to visit The Hall
Click GC4BEPY to visit The Ballroom
Click GC4BEPZ to visit The Conservatory
Click GC4BEQ1 to visit The Library
Click GC4BEQ4 to visit The Billiard Room
Click GC4BEQH to visit The Kitchen
Click GC4BEQ8 to visit The Lounge
Click GC4BEEQB to visit The Dining Room
Click GC4BEQD to visit The Stairs
Click GC4BEP6 to visit The Study
Click GC4BER2 to visit The Garage
Click GC4BER8 to visit The Dumb Waiter
Click GC4BERB to visit The Desk
Click GC4BEQY to visit The Cupboard
Click GC4BEQR to visit The Book Shelf
Click GC4BEQV to visit The Attic