Twilight and her friends bring Phillip Finder to Canterlot to celebrate the Blue Moon Festival. To Twilight's surprise, Flash Sentry is also in town, having recently been transferred to the City Guard as an Investigator.

But the festivities are marred by a series of mysterious burglaries and the suspicious death of a train conductor. Phillip and Flash investigate, and soon uncover a plot to destroy Canterlot, which they may be too late to stop...

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The Phillip Finder series
The Pony in the Gray Trilby
The Everfree Forest Affair
Time Flies
The Blue Moon Brings Death
Letters to a Candymare
The Face in the Darkness
Checkmate
Secret of the Mare Lisa
The Sun Falls
Clockwork
Behind Locked Doors
Siege of Clovenworth
The Silent Fugitive
Curse of the Taverneigh Blue
Mystery on the Mareish Moors
The Grilled Cheese and the Muletese Falcon
Trifle Not With Monsters
The Fillydelphia Solution
The Sydneigh Ritual
Endgame