Let’s take a moment to unpack this (relatively) long sentence. One hour later. Another way of expressing this might be Afterwards by one hour. The Adverb postea on its own has the meaning of afterwards. If, however, we wish to say afterwards [by a certain Period of Time] then the Adverb post is used, surrounded by the Time Period in the Ablative Case. Our story has jumped forward by one hour, hence una post hora, one hour later.
on the roof is a Prepositional Phrase, consisting of the Preposition in followed by the Noun tecto roof in the Ablative Case. in is one of the most interesting of the Prepositions. Followed by a Noun in the Accusative case, it can mean either into or onto. Followed by a Noun in the Ablative Case, it can mean either in or on. So, in tectum could mean into the roof or onto the roof. in tecto, meanwhile, could mean either in the roof or on the roof. Context will hopefully allow you to tell. A notable exception is in used with the verb pono, ponere, posui, positum to put or place, where we might expect the Accusative but instead find the Ablative. pecuniam in sarcina pono. I put the money in(to) the suitcase.
of the neighbouring building. This requires a straightforward Possessive Genitive. The Genitive has only as handful of roles, and expressing Possession is arguably its most important. English does this with the Preposition of or an apostrophe s. The Genitive of aedificium is aedificii. And, as any Adjective must Agree With (i.e. have the same Gender, Case and Number as) the Noun it is describing, the form we are looking for is proximi neighbouring.
that woman, already known to you. With that woman, we finally arrive at the Subject of the Verb and Sentence. The Subject of a Verb is expressed in the Nominative Case. Meanwhile, the Demonstrative Pronoun ille that, like an Adjective, must Agree With the Noun it is describing. Hence, illa femina that woman. known is expressed with the Adjective nota (which, of course, Agrees With femina). But known to whom? Certainly not to anyone who is not yet reading Legonium. But known to you! The term grammarians use for this is a Dative of Reference, because it is written or spoken in the Dative Case and tells us to whom the statement refers. The Dative of tu you is tibi. The Adverb iam means now or already.
more or less. Let’s be honest. We don’t know all that much about this woman. She has so far slipped in and out of the story without giving too much of herself away. plus minusve is found inscribed on numerous Roman tombstones to indicate that the exact age of the deceased is unknown. It means more or less. plus and minus are the Comparative Adverbs more and less, respectively. The –ve attached to the end of the second word means or.
was intently watching the small room again. This woman – don’t worry, we will learn her name soon enough – was last seen watching this small room in Episode 3 – Pico. Hence the Adverb iterum again. The Syllable ba in spectabat indicates that this Verb is in the Imperfect Tense, a Tense that describes ongoing or repeated action in the past. The t at the end indicates that the Verb is Third Person and Singular, which it must be to agree with its Subject femina. The Adverb intente intently tells us the Manner in which the woman is carrying out the Verb. And finally, parvum cubiculum the small room is in the Accusative Case. This is because the key role of the Accusative Case is to indicate the Object of a Verb, and the small room is the Object of was watching.
On hour later, on the roof of the neighbouring building, that woman, already known to you (more or less), was again intently watching the small room.
