FlashTVNews has the description for “Three Ghosts”, the second part of Barry Allen’s two-part guest spot on Arrow.
OLIVER IS VISITED BY GHOSTS FROM THE PAST — After a fight with Cyrus Gold AKA the Acolyte (guest star Graham Shiels), Oliver (Stephen Amell) is drugged and left for dead. Determined to cure him, Felicity (Emily Bett Rickards) makes a risky decision. The cure causes Oliver to hallucinate, and what he sees forces him to confront his past. Meanwhile, Barry (guest star Grant Gustin) continues to help Felicity, and their connection grows stronger. The Arrow asks Lance (Paul Blackthorne) to look into Gold, but when the stakeout on Gold goes bad, someone is killed. Roy (Colton Haynes) is captured and tortured by Brother Blood (guest star Kevin Alejandro). John Behring directed the episode with story by Greg Berlanti & Andrew Kresiberg and teleplay by Geoff Johns & Ben Sokolowski (#209).