[5] The central pediment is ornamented with a carved coat of arms, and the facade is articulated by rusticated quoins.
[5] Due to the lie of the land, the basement storey is exposed to view on the west side of the building, which is constructed in brick with stone quoins and segment-headed windows.
[6] North-west of the house are early 18th-century stables, a dairy barn, walled enclosures and courts, one of which formerly served as a wood yard.
The south face of the north wall of the Mount Garden is constructed with recessed arcading for espaliered fruit trees.
The rectangular area with its perimeter walk was originally subdivided into three sections by two internal walls running from east to west across it.
The present wall which screens the garden from George Lane is a late 20th-century reconstruction, necessitated by widening of the road beyond.
The pattern of burgage plots suggests that it did not but it might reasonably be expected that some development would have occurred to the east of the castle, in the vicinity of the church.
As related below, there were however buildings on the site before 1700, the most likely location being along the frontage at the lower end of George Street and into Longcause, and archaeological evidence of them may survive.
He had been baptised at Plympton St Mary, the son of Peter Treby "Gent" and after attending Exeter College Oxford studied law at Middle Temple and was called to the Bar in 1671.
He held other important offices and was knighted in 1680 but fell from favour in 1683 and took little part in public affairs until the landing of William of Orange in 1688, following which he rose rapidly again, becoming Lord Chief Justice in 1689.
[8] He had plans for the house and grounds and had cleared the site but had made little progress with the building work at the time of his death.
[8] The Treby family's estate in the environs of the ancient Borough of Plympton, the Rotten Borough parliamentary constituency of which was known as Plympton Erle, was expanded following the marriage of Judge Treby's father to his mother Joan Snelling, daughter of John Snelling of Chaddle Wood, Plympton (which mansion house survives today after early 1800s rebuilding),[9] and co-heiress to her nephew Francis Snelling.
Of the landed estate formerly attached to Plympton House, only an early 18th-century formal garden of 3 hectares remains.
[3] In 1811, Risdon described the house merely as the property of Paul Treby[13] and in 1821 a guide book, The Panorama of Plymouth, says it was "at present uninhabited".
A recessed gateway had been formed and tree planting introduced replacing the yard to the west of the chapel garden.
[3] In the 1990s the c. 1960s extension on the east side of the house was enlarged and remodelled, with associated landscape works including vehicle access from the south garden.
[3] In 2012 St Peter's Care Home closed,[18] when the 44 bedroom Plympton House, with significant modern additions including an accommodation block and a convent with its own chapel, in all 2984 sq.m (32118 sq.ft), was offered for sale with 5.6 acres of surrounding gardens.
The website stated: "The concept is to return the site to a low density residential usage that allows the main house to be restored to its former glory but in a way suitable for use in the 21st century, all the while enhancing the village of Plympton-St-Maurice.