in (one's) train
old-fashioned In pursuit of someone; following closely behind someone. They were forced to flee the country in their benefactor's train, facing persecution at home and having no resources of their own abroad.
In motion; in progress; currently being prepared, processed, or dealt with. The article, which featured allegations from over a dozen ex-employees, set in train a series of lawsuits, firings, and investigations against business leaders accused of violating numerous tax codes. As construction is already in train, there is no point protesting against it; rather, we should refocus our energy to make sure the project is held accountable to the highest level of public scrutiny.
in train(of arrangements) in progress; being proceeded with.
2005 Architectural Review ‘China's New Dawn: an Architectural Transformation’ is a mainly pictorial survey of some 50 projects, recently completed or in train.