The man and the woman were caught in an "objectionable condition" in the house in Golra area yesterday.
Police said the man hired a sex worker and brought her to his friend's home, the Dawn newspaper reported.
The man was spotted by residents of the area, who assembled outside the home and broke into it and found the man and the woman in an "objectionable condition".
More than 20 people beat the three persons with iron rods and batons.
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One of the injured died later in hospital, while the condition of the sex worker was described as critical.
The other man was in a stable condition.
Police arrested two persons involved in the attack.