Contains spoilers for this episode and earlier episodes.
Lightman's holiday in Mexico with Emily becomes an investigation when an American mother disappears. Her daughter remains behind, and Lightman refuses to accept the easy suggestion that the missing woman simply abandoned her. Another disappearance and questions about how the women could afford their holidays lead towards an egg-donation business. A Canadian couple's frozen embryos provide a connection between the missing mother and a broker selling anonymous donors.
Lightman poses as a prospective client and tests the supposed doctor's knowledge with a deliberately absurd explanation of infertility. The man's agreement exposes him as a fraud. The broker has been recruiting women who need money while inventing desirable backgrounds for buyers. The missing mother suffered internal bleeding during a botched extraction and was hidden in an apartment. Lightman finds her in time for treatment, and she is reunited with her daughter.
Back in Washington, Gillian works with Lightman's rival Jack Rader after several patients become critically ill following transfusions. Interviews with hospital staff produce little until recordings reveal equipment that disappears during a break. Searching the laboratory exposes an illegal drug operation, explaining the contamination behind the medical emergency. Gillian and Rader solve the case together while Cal remains abroad. Emily's holiday is disrupted, but she sees her father stay with the search until the other daughter gets her mother back.