The CW has released an official description for the fourth episode of The Flash, and they’ve now updated the write-up to include the guest appearance of Emily Bett Rickards as Felicity Smoak.

Here’s the write-up:

WENTWORTH MILLER GUEST STARS AS DC COMICS’ VILLAIN CAPTAIN COLD; FELICITY FROM “ARROW” CROSSES OVER INTO CENTRAL CITY — The Flash (Gran tGustin) stops a robbery but the culprits get away after shooting a guard, and The Flash chooses to save the man instead of following the criminals. Joe (Jesse L. Martin) shows Barry a book of suspects and Barry identifies Leonard Snart (guest star Wentworth Miller, “Prison Break”) as the leader of the group. While investigating the case, Barry gets a surprise visit from an old friend –Felicity Smoak (Emily Bett Rickards, “Arrow”), who heard about his new abilities and came to check them out for herself. She joins him at S.T.A.R. Labs to help stop Snart after it’s revealed that Snart his gotten his hands on a stolen “cold gun,” which could kill The Flash. Dr. Wells (TomCavanagh) is furious when he finds out that Cisco (Carlos Valdes) built the cold gun without telling anyone and now it’s missing. Meanwhile, Iris (Candice Patton) is getting the silent treatment from Joe because of her relationship with Eddie (Rick Cosnett). Finally, The Flash and Captain Coldhave an epic confrontation. Glen Winter directed the episode written by Geoff Johns & Kai Yu Wu(#104). Original airdate 10/28/2014.