The 100th episode of "Arrow" is going to be huge. Packed with guest stars, it seems like every major character will be making a return. We already know that Katie Cassidy will be returning as Laurel Lance. Stephen Amell recently revealed via Twitter that his nemesis Deathstroke will be making an appearance. We even know that Queen family patriarch Robert will be making his return. The guest stars don't stop there though; it seems that Moira Queen will also be making an appearance.

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As reported by Entertainment Weekly, actress Susanna Thompson will be returning to the show -- her first appearance in quite a while. There seems to be a theme to most of these guest stars, however: Nearly all of them are dead! Moira was brutally murdered by Deathstroke towards the end of "Arrow"'s second season. It is unknown whether her return has any connection to Manu Bennett's Deathstroke.

This leaves fans with plenty of questions. Arrow has never shied away from flashbacks, but is there something more going on in this landmark episode?

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Starring Stephen Amell, Emily Bett Rickards, Willa Holland, David Ramsey and Echo Kellum, among others, the fifth season of “Arrow” premiers Oct. 5 at 8 p.m. ET/PT on The CW. The 100th episode is expected to air in December as part of the crossover with “The Flash,” “Supergirl” and “DC’s Legends of Tomorrow."