Gallen Lo and Chan Sao Mun are happily married and have a son together. Gallen is a cop while Mun used to be a famous reporter but has decided to stay at home ever since their son was born. Lum and Maggie are Vietnamese who came to Hong Kong as refugees and they were later recruited by Lam Seung Mo's organisation as hitmen.

Mun returns to work at the news agency and is involved with the investigation of Mo's organisation. Feeling threatened by Mun's probing, the organisation orders Mun's death. Maggie is assigned to do the job. Mun is killed during an outing with her son, and when he rushes out to his mother, he too is killed by an oncoming car.

Gallen is devastated by his wife and son's death. Maggie becomes a witness to a murder believed to have been carried out by the same person who killed Mun. Gallen and his team are assigned to protect her until the killer is caught. During their time together, Gallen and Maggie slowly falls in love. What will happen when Gallen finds out that the person responsible for the death of his wife and son is actually Maggie?