S1·E271 The Case Of The Red Rain - Part 1

An elderly gentleman is seen driving the car erratically and dashes against the sidewalk. He gets out of the car and after taking a few unsteady steps fall down dead. CID finds out that it is not a case of drunk driving but a cold blooded murder as someone had injected him with poison. It also transpires that he had got a unsigned letter giving him a death threat. His two other business partners too get killed with the same poison just after the funeral.