The premiere of Zero Hour (1.3/4) on Valentine’s Day saw the full-time return of Anthony Edwards to primetime more than a decade after he left ER. Unfortunately for ABC, on a night that traditionally sees lower viewership, the conspiracy drama marked the lowest-rated in-season debut for a scripted show ever on the network. Facing off against American Idol in the 8 PM time slot, Zero Hour was down 41% from the September 27 premiere of Last Resort, a show that is now cancelled, and 38% from the March 15 premiere of Missing. That still pales compared to the January 31 premiere of the now cancelled Do No Harm on NBC which got a 0.9/3) and was the lowest rated in-season premiere ever of any scripted show on the any of the Big Four networks.

Zero Hour wasn’t the only show having a rough night. In its second week of its fourth season and also head-to-head with Idol on Fox, NBC’s Community (1.1/4) fell 42% from its season debut last week to hit a series low. ABC’s Grey’s Anatomy (2.7/7) didn’t have to face Idol, but it was down 13% from last week to also hit a series low. In its second show of the Girls Only Hollywood Week, Idol (3.6/11) itself was also down. The competition series slid 12% from last week’s Guys Only Hollywood Week Part 2 show. Following Idol, a new Glee (1.7/5) took a bigger hit, falling 23% its February 7 show.

The most watched show of the night, The Big Bang Theory (5.4/17) pulled in 17.63 million viewers on CBS last night but was down in the demo 13% from last week. Two and a Half Men (3.8/11) was dipped 7% from its February 7 show and Person of Interest (3.0/8) slipped a slight 3% too. Elementary (2.2/6) was flat with last week’s show. ABC’s Scandal (2.8/8) was flat with last week’s show but for the first time in its history the political drama built on its Grey’s lead in. Scandal won the 10 PM time slot in the key 18-49 demo. Elsewhere on NBC on Thursday, Parks and Recreation (1.5/5) fell 25% from its show last week while The Office (2.0/6) was down 5% Slotted to replace Do No Harm, a Law & Order: SVU(1.0/3) repeat ended the night for NBC. On The CW, The Vampire Diaries (1.0/3) was down a tenth from its February 7 show as was Beauty And The Beast (0.5/1) CBS topped the night in both overall viewers and among adults 18-49.

Deadline's Dominic Patten - tip him here.