Phineas Pratt was your immigrant Pratt ancestor. Here is his story:
Phineas Pratt was born in England, probably in London, about 1593. It is thought that he had a brother Joshua, also an early settler in Massachusetts, and that their father was Henry Pratt (b about 1545). Henry Pratt was a minister "imprisoned in England because he preached the Gospel contrary to the rules of the established Church." It is believed Henry's father was named John.
Phineas arrived in Plymouth in May 1622 on the ship Sparrow. Six men arrived in Plymouth but this group had not come as colonists for Plymouth. Six months later they joined others from the ship Charity and the ship Swan, all three groups sent out by the Pilgrim's opponent Thomas Westin, for the purpose of establishing a rival colony at Wessagusset (present day Weymouth near Boston).
This colony was doomed to failure. They made enemies of the Indians and were a "...reckless and improvident lot who quickly made havoc of their provisions." They finally precipitated a minor war with the local Indians. When the aroused Indians threatened to attack the disorganized colony Phineas fled to Plymouth. Stories vary about his motivation. Some say he was just escaping, others (which I tend to believe) say he was running to Plymouth to warn them of a planned Indian attack on all the English.
One story goes: The Pilgrim's apprehesions were reinforced by the unexpected arrival of Phineas Pratt with a small pack on his back. He managed to get to Plymouth from from Wessagusset, though he had not the slightest idea of the way (My Note: He had been to and from Plymouth before but only by boat) and had gone off course several times, which was a good thing as the Indians had been after him. Pratt's advice was simple: he dared not stay with the Pilgrims, because from what he had been able to observe, they would all be knocked in the head shortly unless they did the sensible thing and left. Soon afterward one Indian who had been chasing Pratt came through Plymouth "still pretending friendship". Taking no chances Bradford (the leader of the Plymouth colony) lodged him in the fort, chaining him to a post where he would have to be content to remain until Standish got back from Wessagusset.