The Room Where it Happened. Operation Quickline, #14

The job was a nuisance. The target was a disasterSid Hackbirn never knew his mother Sheila. When startling new evidence in Sheila's murder shows up, Sid isn't terribly interested until Stella, the aunt who raised him, becomes hellbent on finding out who killed her sister over thirty years before. As undercover agents in a top-secret organization, Sid and his wife Lisa Wycherly have the skills to investigate, but then get assigned to watch a congressman who was one of the main suspects in Sheila's murder.
With the congressman trying to make Sid into the son he should have had, and Stella recklessly diving into questioning suspects, Sid and Lisa are up to their armpits in a case that stands little chance of putting the demons of the past to rest.