Moliarty, the fiendish genius marketer and mole from the deep underground, has rallied his fellow race for an attack to takeover the surface city of St. Canard. Stealing buildings, he creates a beam to lock the moon in an eternal eclipse - to plunge everything in darkness.
"The city of St. Canard is home to a thousand criminals, but not one dares make a move. For this city has a shadowy guardian who hunts them like a phantom in the darkness. I am that guardian. I am the terror that flaps in the night! I am the winged scourge that pecks at your nightmares! I am Darkwing Duck! And I am... totally bored out of my skull!"
— Darkwing Duck.
"Is someone laughing at me. I hate that."
"I am the terror that flaps in the night! I am the winged scourge that pecks at your nightmares! I am Darkwing Duck!"
— Moliarty and Darkwing Duck.
"Moliarty! It's Darkwing Duck!"
"Please, I'm eating. This isn't a time to discuss slug lunches."
"But he is loose and attacking our troops."
"WHAT! This isn't a joke, is it? I would hate that."
"The daring Darkwing Duck defies death yet again, and defeats the despicable denizens of darkness!"
It's amazing my brilliance doesn't blind people.
Darkwing's "It's like the chicken says, Launchpad, I knew the job was dangerous when I took it!" is a reference to a running gag in the 1967 cartoon Super Chicken. Super Chicken would tell his colleague Fred when he accidentally injured him: "You knew the job was dangerous when you took it, Fred!" The same reference is also made in "Darkly Dawns the Duck, Part 1"/"Darkly Dawns the Duck".
This episode was made into a children's book under the same name.
"That Sinking Feeling" is the very first Darkwing Duck episode to be written and animated. While never meant to be a first episode, as evidenced by the production number of 4308-007, it is a pilot episode in itself, existing next to "Darkly Dawns the Duck". Because of its early production placement, several details that were created during the concept phase, but adjusted during development are present here in their original form. For instance, Darkwing's intro speech is played straight and doesn't change between its two iterations, because Darkwing always coming up with a funny second line came from the development of "A Duck by Any Other Name". The gas-based ammunition variation gets much more emphasis here than in any other episode, and this is the only time in the cartoon that the lack of labels on the gas cans is brought up.