JAKUB Sokolik has become Argyle's first signing of 2017.
The defender – the first Pilgrim from the Czech Republic – comes to Home Park after being released by Sky Bet League One Southend United last month.
Jakub, 23, is former Liverpool junior who has also had League One spell with Yeovil Town since leaving Anfield in 2014.
He will wear the number 31 shirt but is not eligible to play in Sunday's Emirates FA Cup third-round tie at his old club, having represented Southend against Millwall in the first round of the competition.
Jakub came through the ranks of the Anfield Academy after being signed by Rafa Benitez from Banik Ostrava as a 15-year-old on the advice of Liverpool's chief scout Eduardo Macia.
He failed to make a first-team appearance for the Reds but had a 10-game loan spell at Southend United, then in League Two, before leaving Anfield for Yeovil on a two-year deal.
He played 45 times for the Glovers over two seasons, either side of a loan back to Southend, although his progress was initially hampered by a knee injury.
After 40 games in all competitions last season, including two against the Pilgrims in Sky Bet League Two, he returned to Southend for a third spell at Roots Hall on a short-term deal.
The last of nine appearances for the Shrimpers came on December 10, as a late substitute in a 3-1 home win over Coventry City.