Looking back into the earlier comments on Castle, I see that Cass figured out Jonathan Adams (Vulcan Simmons) before any of us.
He was just the start of my, "OMG, the guest stars in this ep, duuuuuuuuuude..." night.
Really I had to imdb him because his voice grabbed into my head, made me look up and then he looked different than my brain expected that voice to look. It was a good night for voices my brain liked.
Apparently all Angela Cass needed was to hear her job description the guest star talking in a deep African-American tone.