Police are investigating an aggravated robbery at Plympton this morning. At about 11am today, a man armed with a knife entered the post office on Marion Road and demanded money. He fled with an amount of cash, and was last seen running north on Marion Road. No one was injured during the incident. The man is described as being of Caucasian appearance, aged in his 40’s, about 160cm tall, black hair, clean shaven, and was wearing a grey and black tracksuit top, and a black beanie