How is the underlined pronoun used in the subordinate clause?

I want to meet whoever wrote that anonymous article.

a. object of a preposition

b. indirect object

c. direct object

d. subject

The pronoun whoever is used as direct object in this sentence.

It cannot be an object of a preposition, since there is no preposition in front of it.

It isn't indirect, because, again, there are no prepositions.

And it isn't subject, because the subject is the pronoun I.