Tierney had set up residence in the Northern Valley, a region in New Jersey. Tierney was licensed by the state as a crime investigator. Paddy Fallon, a friend of Tierney's, asked him if he considered moving to a more lively place than the Valley where his saved money could work for him. Perhaps, according to Fallon, Tierney could set up shop selling fishing tackle in the Sahara Desert.
Later, Tierney and his squad tailed Forrester as he was chauffeured along Twenty-third Street to Fifth Avenue, en route to his final destination, the posh hotel known as the Plaza. Tierney's squad had bugged the room that Forrester was staying in and listened to his phone conversations from their room on the eleventh floor.
Some nights later, after Forrester eluded had them, Tierney left a police station and headed to Park Row and Gold Street while on assignment to inspect junk shops. While walking down the street, he paused in front of the World Building and watched the commuters heading home.
Tierney was posted to the Oak Street station. During his first year at this station, he worked as a plainclothes man. One night, he had arrested Dolan, a powerful and well-connected man, for taking money for a drink on Sunday. According to the law, there was a prohibition on selling alcohol on a Sunday.
On one New Year's Eve, Tierney had his fellow officers posted at the Trinity Church. They were to keep the peace, and arrest petty criminals and bullies.
According to Tierney, the criminals were one step ahead of the police when it came to technology. In his opinion, when Henry Ford was hardly out of short pants, instead of riding horses, the criminals were driving about in automobiles. (TNG: "The Big Goodbye")