Speak to PAM at The Railroad base who will tell you about a synth stuck at Memory Den, unable to escape. Travel to Goodneighbor and speak with Doctor Amari in the Memory Den and inform her of the plan. You may opt to obtain the holotape from H2-22.
Head to Malden Center in the northern Commonwealth to eliminate the Gen 1 Synth group who is preventing the Railroad's runners from getting H2-22 out. Glory, a Railroad agent will meet you at the door. You may take her with or go it alone.
Once inside Malden Center, kill all the synths marked on your Pip-Boy. You may optionally kill the Raider group here. Finish the task and return to Desdemona for your reward of caps and a Railroad Stealth Boy x2. The Railroad stealth boys can also now be purchased from Tinker Tom.