The Invisible Train is a global transportation network used by various freight companies such as Dagan Logistics to ship items all over the world in secrecy from the mortals.
The Invisible Train is a magical train capable of travelling on underwater rails which is hidden from the mortal world by cloaking spheres in each carriage. It is unkown where it is loaded with supplies although it is implied by Skulduggery Pleasant that it is an 'Express Service' and therefore never stops although this calls into question how supplies are loaded onto the train.
Valkyrie Cain, attempting to find Tyren Lament through shipment orders placed by him with Dagan Logistics, decides to obtain the information through Hansard Kray, son of Dagan Logistics owner Arthur Dagan whom learned was on the train personally overseeing a shipment. Arriving on the train, she finds out that the shipment consists of an improved version of Hollow Men. In a panic she attacks them and loses consciousness. She awakes after Hansard found her and explains that Hollow men are not evil and are also used for cheap labour and security. She obtains the information after flirting with him. As she leaves she tries to give him her phone number and is mortified when he declines.