"주인은 거짓말을 하자고 했어요."
Translation:The owner said let's lie.
말 (noun) = word
말 (“word”) + 하다 (“to do”) --> 말하다 (verb) = speak, talk
거짓 ("untruth") 말 ("word") = untrue word = lie (noun)
"을" in 거짓말을 is a marker to indicate the noun "거짓말" is a direct object complement (often described as "Object" to contrast with "Subject" in a sentence.).
feel the 주인 you are talking about would be "master". Correct me if i am erong, but i feel that you are not the one being owned when you say owner. the sentence doesnt specify what the owner owns, but if you say he owns the house that you are living in, we tend to call them 집주인, which roughly translates to house owner.