the "fifth guest" is Tom's mistress who arrives unexpectedly. The "fifth guest" is the butler who takes a seat at the table. What did Jordan Baker tell Nick Carraway about Tom Buchanan? She told him that Tom is terminally ill.
Technically there are only two tenses in the English language. The Past tense and the Present tense. The future isn't a tense because it has yet to happen, thus it is time that may never happen and is bound to change. Aspects however can apply to tenses such as the progressive aspect (more commonly known as the continuous) or the perfect aspect. Thus in combination of both tense and aspect, we get an understanding of the temporal occurrences of activities.