Is there a spell or item that can detect Lycanthropes while they are in their human form?

Since purchasing the Troll Skull Tavern in Waterdeep, Ichabod the Inscrutable has run afoul of the Shard Shunner wererat gang. He believes their leader to be none other than the Fellowship of Innkeeper’s guildmaster, Mister Fairkettle.

Obviously, Ichabod can’t just run to the Watch, some of them are likely on Fairkettle’s payroll! What magical means are available to him that would help him identify and prove who the wererats are?

Ichabod has access to any published, core (non-UA) item or spell that is not an artifact or 9th level.

Is there a spell or item that can detect Lycanthropes while they are in their human form?


This question is purely hypothetical. Any resemblance to characters, living or dead, actual or fictional, is purely coincidental and is in no way intended to be a spoiler.