intriguing

Causing a desire to know more; mysterious.

As a result, while the train was being shunted at Bombay, the buffers became locked, producing a situation most intriguing for the onlookers, but exasperating for the exalted passengers and the unhappy railway authorities.

Involving oneself in secret plots or schemes.

A book that does not sell us the powerful, intriguing women of Rome simply as poisoners, schemers, and femmes fatales […]

Having clandestine or illicit intercourse.

[…] few respectable women will now sit at a window, looking into the public street, or gaze at passengers in any large town or city; and no one does so at present, unless an innocent inexperienced, husband-hunting, flirtish, or intriguing person.

An intrigue.

In all these negotiations, and caballings, and intriguings, the person most concerned, Frances Coke, the beauty and the heiress, was only the ball in the game.