The Metal Island is a pocket plane that could be reached by using the Riddle Gate on Esper.
On this plane, Tezzeret tried to defeat his former employer Nicol Bolas.
When Nicol Bolas arrived, unaware of Tezzeret's newfound capabilities, he began to demand answers regarding Tezzeret's search for etherium. Baltrice arrived next, along with Jace Beleren, followed lastly by Sharuum, stripped of her etherium. As soon as she left again, a terrible fight broke out among the assembled walkers, and it ended with Bolas apparently victorious. However, during the fight, his concentration and powers severely waned. This was revealed to have been engineered by Tezzeret, who was the true victor of the fight. He resuscitated Baltrice and Jace, giving Baltrice a sangrite necklace which would undo the mental tampering that Jace had been forced to use to save her. Jace fled and Tezzeret left Bolas trapped on the island.
However, Bolas had predicted all of Tezzeret's actions and sent a mere simulacrum to the island.