[This is a review of Arrow season 2, episode 15. There will be SPOILERS.]

Early on, the island flashback sequences on Arrow largely served as a sort of novelty; a clever way of tracking Oliver’s progression from spoiled rich kid, to the hero is today. Generally, they were best used as a supplement to the present day storyline, matching the emotional tenor of Oliver’s adventures in Starling City with some similarly resonant event from the past. But when the show served up ‘The Odyssey‘ last season (a bottle episode that effectively turned Slade Wilson into a major player in the Arrow universe), and when it was revealed that many of the individuals from the island weren’t simply relegated to being flashbacks themselves, the significance of the sequences went from being a simple additive, to finally being the other half of the story.

In fact, in ‘The Promise,’ the narrative of the episode is closer in structure to the aforementioned ‘The Odyssey,’ in that the present day element serves to supplement the action that’s taking place on the island. As has been seen before, doing that requires a significant event to take place. Last season, it was Oliver and Slade’s team up to take down Edward Fyers; it was the first step in Ollie’s progression toward becoming Arrow, and here, the episode demonstrates just how quickly things go from bad to worse once Slade is made aware the truth behind Shado’s death.

That affords the episode a thrilling set piece, involving Slade, Sara, and Oliver storming the Amazo, in order to eliminate Dr. Ivo (Dylan Neal) and hopefully secure his vessel as a means of escape from the island. Naturally, despite Sara thinking far enough ahead to provide Ollie with a mixture to combat the effects of sodium pentothal, things don’t necessarily go as planned. When Oliver corners Ivo, the doctor goes into a frantic speech about Oliver choosing Shado’s death when he opted to save Sara, attempting to shift the blame from himself. When Slade overhears the conversation, he immediately turns on Oliver. Slade manages to take control of the ship, make Oliver his prisoner, and separate Ivo’s right hand from the rest of his body. Meanwhile, Sara finds herself separated from Ollie, after she winds up back on the island and in rather strange company.

It’s never a good sign when it takes as much verbal gymnastics as it did to demonstrate Ivo’s shifting of the blame for Shado’s death onto Oliver, so the less the series says about that in the future the better. Thankfully, though the impetus for his rage doesn’t feel as compelling as might otherwise be , at least the writers can blame the majority of Slade’s unhealthy preoccupation with meting out revenge against Oliver and his family on the mirakuru in his bloodstream.

Some tricky characterization issues aside, ‘The Promise’ works terrifically on an action level, while also serving to arrange the next phase of Arrow‘s dual storylines. While Slade’s touring the Queen art collection (and setting up a system of spy cameras), the rapid response and assembly of Team Arrow winds up being one of the more tension-filled components of the episode. As the title suggests, the events are merely a warning of dangers yet to come, but the sight of Roy, Sara, and Diggle coming to Oliver’s aid suggest those dangers may be bigger than anything Arrow has previously encountered.

Arrow continues Wednesday, March 19 with ‘Suicide Squad’ @ 8pm on The CW. Check out preview below: