All 5 Uses

inquiry
in
The Phantom of the Opera
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The truth was slow to enter my mind, puzzled by an inquiry that at every moment was complicated by events which, at first sight, might be looked upon as superhuman; and more than once I was within an ace of abandoning a task in which I was exhausting myself in the hopeless pursuit of a vain image.†
Chpt Prol.

inquiry = questioning or investigating
In this connection, I should like to print a few lines which I received from General D——: SIR: I can not urge you too strongly to publish the results of your inquiry.†
Chpt Prol. *
And I should be ungrateful indeed if I omitted, while standing on the threshold of this dreadful and veracious story, to thank the present management the Opera, which has so kindly assisted me in all my inquiries, and M. Messager in particular, together with M. Gabion, the acting-manager, and that most amiable of men, the architect intrusted with the preservation of the building, who did not hesitate to lend me the works of Charles Garnier, although he was almost sure that I would never return them to him.†
Chpt Prol.

inquiries = questions or investigations
For the moment, M. Mifroid's inquiry saved them from any such unpleasant encounters.†
Chpt 20

inquiry = questioning or investigating
Day by day, I kept him informed of the progress of my inquiries; and he directed them.†
Chpt Epil.

inquiries = questions or investigations

Definitions:

(1) (inquiry)
a question or investigation -- especially one meant to gather information or find out the truth
(2) (meaning too rare to warrant focus)