In Hong Kong, Circa 1940s, World War II, private detective Yoyo and friend Inspector Teddy Robin join a resistance group during the Japanese occupation. They aim to steal back the formula to the atomic bomb from a war traitor and transfer it to an American before the formula ends up in the Japanese emperor's hands.

Little Tiger ventures from the sticks to the big city in search of his cop brother Big Tiger, an honest cop working in a corrupt system. Surmising that life in the police force was not his cup of tea, Little Tiger joins the Swallow Acrobatic Troop, which he excels in because of his kung-fu prowess. When a band of thugs from Chin Hung-yun's group attacks the troop, Little Tiger not only handily fights them back but also infiltrates their organization to destroy them from the inside. Meanwhile, Big Tiger's old flame Mary returns from America to join the revolutionaries. Big Tiger soon finds himself torn between his love of this girl and his orders to arrest all revolutionaries.

“小飞象”陈初（洪金宝 饰）自幼习武，身手矫健，在打劫了一家财务公司获得了巨款之后，他决心金盆洗手，回归平静的生活。“猫头鹰”黄人富（林子祥 饰）谙熟处世之道，头脑精明聪慧，设计骗得了黑心商人欧根非法获得的赃款之后亦决定洗心革面，不再出山。
一晃眼三年过去，远离江湖的陈初开起了健身馆，生意经营得风生水起，而黄人富亦依靠之前积累的财富，过着衣食无忧的生活。一封不期而至的神秘信件彻底打破了两人闲适的生活，信中揭露了他们不为人知的的过去，并以此要挟他们重出江湖，否则就要将信件的内容公之于众。无奈之下，陈初和黄人富只能再度联手，和幕后的黑手进行殊死搏斗。