The May 1 episode of The CW's Arrow sees flashbacks to a time before Oliver was on the island, and folks like John Barrowman, Colin Salmon, and Jamey Sheridan are all along for the flashback ride.
Here's how The CW describes the episode, which is called "The Undertaking."
WITH A LEAD ON WALTER'S WHEREABOUTS, OLIVER GAMBLES ON FELICITY IN THE FIELD --- Finding it difficult to mend fences with Tommy (Colin Donnell) and Diggle (David Ramsey), Oliver (Stephen Amell) instead focuses on crossing another name off the list. While digging through a crooked accountant's laptop, Felicity (guest star Emily Bett Rickards) discovers a transaction that could help Oliver find Walter. To reconfirm the lead, Oliver gambles that Felicity can be counted on in the field for the first time. In a flashback, Malcolm (guest star John Barrowman) reveals to Robert Queen (guest star Jamey Sheridan) and Frank Chen (guest star Chin Han) painful details surrounding his wife's murder, and how that shaped his plans for the Glades. Meanwhile, Tommy (Colin Donnell) stuns Laurel (Katie Cassidy) with the truth. Willa Holland and Susanna Thompson also star. Michael Schultz directed the episode written by Jake Coburn & Lana Cho (#121).
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