The issue mostly focuses on the Viltrumites, the alien race that Invincible and his father belong to. We do not learn anything new about the culture this time; however, Invincible and his father are brought up to speed on things we have been aware of for a while now.
Grand Regent Thragg (a cross between General Zod and Denethor who bares a striking resemblance to Freddie Mercury) is the current ruler of the Viltrumites. He came to power after Lord Argall, the previous ruler, was killed and his heir was hidden. Since then, Thragg was tasked with leading the empire until he could find the lost heir. Back in Invincible #89 when Thragg helped to save Invincible from the Scourge Virus, he discovered that Invincible's father Nolan is Lord Argall's missing son—making him the rightful ruler of their race.
A year after we learned this information, the secret is finally out. The consequences of this issue will propel Invincible comics into their next major chapter. After Issue #100, we have been wondering what new direction Robert Kirkman was writing for us, and we are now finally getting an idea of what that is.
It is also worth noting that this issue is almost the exact opposite format of a typical comic book. Instead of starting slow and building to a big action sequence, it opens with a fight and concludes with an intimate and personal scene. This quiet moment ends the issue on a high note and leaves the reader excited for what is yet to come.