[4x20 Spoilers] 'Genesis' Official Description

DIGGLE IS CONSUMED WITH GUILT AND SEEKS REVENGE – As Oliver (Stephen Amell) and Felicity (Emily Bett Rickards) look for a magical solution to defeat Darhk (guest star Neal McDonough), a vengeance-driven Diggle (David Ramsey) gets a lead on Andy’s (guest star Eugene Byrd) whereabouts and heads off to confront his brother. Meanwhile, Alex (guest star Parker Young) takes Thea (Willa Holland) on a vacation that quickly turns into a nightmare. Gregory Smith directed the episode written by Oscar Balderrama & Emilio Ortega Aldrich (#420). Original airdate 5/4/2016.