Thappu Thalangal is a saga of emotional and selfish world of human feelings. Devu, a local thug whose weapon of choice is a bicycle chain he sports casually around the neck. On one of his nightly rounds, Devu is pursued by a cop and seeks refuge at a whorehouse run by a hooker Sarasu. Despite her vehement protests, he stays put and leaves only at daybreak, but her persistent cough stays with him. At a theatre, Devu watches an advertisement for Glycodin Cough Syrup and proceeds to buy her a bottle. Devu and Sarasu bond over the cough syrup and philosophize late into the night, exchanging notes on their immoral lifestyles. Devu's assault on a trade union leader delivering medicine to a critically ill worker leads to a mishap. In an inspired moment, he suggests they remap their lives and chart a moral course. The couple's plans for normality never attain fruition. The inevitable return to lives of vice is especially tragic and heartbreaking.