In 2253, Tapia was interned with MetaPol on Mars and was partnered with Alfred Bester when the two encountered Endra Nadja, a martian born miner who took a particular exception to the two telepaths. After a brief but vitriolic argument, Ysidra arm was all but severed by a silicon cutter knife thrown by Nadja. Bester quickly took down the miner and was able to save Ysidra's arm, taking her to hospital for treatment.
Some time later, her wound healed but with a scar that she wore with no small amount of pride, Tapia accompanied Bester on a blip hunt to track down her old classmate McDwyer who had escaped from a Department Sigma medical facility. They quickly tracked McDwyer and his trail of bodies to the abandoned hotel Tharsis ahead of Sigma. There they cornered him and Bester tried to talk him down, but was forced to kill him after a crazed attempt to share his insanity with the Psi Cop.